US Foreign Policy

The Use of Military Force

Michael Flynn

Professor

Department of Political Science

011C Calvin Hall

meflynn@ksu.edu

2025-10-29

Lecture Overview

1. What constitutes a “use of force”?

2. Trends in the use of force over time

3. When and why does the US use military force?

4. Constraints on the Use of Force

Key Questions

1. What does US military activism look like over time?

2. What constraints do policymakers face when using military force?

3. What domestic factors shape incentives to use military force?

4. Why do policymakers escalate (or not) military conflicts?

5. What role do concepts like “resolve” play in the use of force?

What Constitutes Force?

Notes:

• Talk about general misconceptions of what constitutes military force
• We typically think of big cases, but most are small.
• If it pops into your mind, it’s probably a bad representative case.

What Constitutes Force?

What do we mean when we talk about the use of force?

• This probably seems obvious, but reality differs from most people’s perceptions

• Most uses of military force are short duration and low intensity

• Large-scale uses of force (i.e. wars) are relatively rare

Allied forces move ashore during the invasion of Normandy, June 6, 1944.

Notes:

• Operation Overlord - The invasion of Normandy on D-Day in WWII.
• Massive multilateral military operation that took months of planning.
• This is a highly salient, but highly unusual example of military force embedded within an already enormous military operation.

Members of the US Marine Corps 15th Marine Expeditionary Unit Maritime Raid Force fight off pirates that seized the Magellan Star in the Gulf of Aiden, September 2010.

Notes:

• US Navy and Marines conduct an operation to retake a ship from pirates in the Gulf of Aden
• This is not Captain Philips, but similar.
• Smaller operation, limited goals

The guided middle destroyer USS Porter launches cruise missiles targeting Al-Shayrat Air Base in Syria. These strikes were part of a larger operation that involved the launch of 59 Tomahawk cruise missiles at targets in Syria in response to the use of chemical weapons by the Syrian government against civilians.

Notes:

• USS Porter launches cruise missiles into Syria in response to reports that Syrian government used chemical weapons against civilians.
• Smaller operation, more limited goals.
• Intent is to signal more than achieve general military goals.
• We’ll talk more about this point later

What Constitutes Force?

What do we mean when we talk about the use of force?

• This probably seems obvious, but reality differs from most people’s perceptions

• Most uses of military force are short duration and low intensity

• Large-scale uses of force (i.e. wars) are relatively rare

Notes:

• Militarized interstate disputes (MID) represents a way to conceptualize a broad range of cases where force is used
• Not all of these are purposeful policy actions
• Many represent impulsive acts on the part of agents in the field

Notes

• What are the patterns here?

Notes

• Broken down by type
• Notice that green and yellow are the most common categories

Notes

• US MIDs relative to all mids in a given year
• US Accounts for a fairly high proportion of total MIDs in any given year.

Notes:

• Notice that most conflicts are very short.
• Mean is less than 6 months,
• Median is only 0.04 years—only about 14 days.
• Side point—this is why stats is handy. Average isn’t always the best indicator to use.

When and Why Does the US Use Force?

When and Why Does the US Use Force?

Motivations:

• Protest citizens abroad
• Acquire territory
• Secure commerce and access to markets
• Secure access to to resources
• Remove hostile leaders/governments from power
• Check expansion of rival powers
• Signal resolve
• Strikes against actors who use terror
• Intervene for humanitarian reasons

Notes

• Countries use force for all sorts of reasons

US military forces occupy the city of Veracruz, Mexico, 1914.

Notes:

• Occupation of Veracruz, Mexico in 1914.
• Began with the arrest of 9 US service personnel who went into a restricted part of the city. They were released a short while later.
• US Admiral Mayo demanded an apology (which he got) and a full 21 gun salute from the Mexican military.
• Victoriano Huerta had come to power in a coup during the Mexican Revolution. President Wilson hoped to push him out of power. Wilson decided to use this as an opportunity to increase pressure on Huerta and backed Admiral Mayo’s demands. Huerta refused.
• Wilson asks Congress for approval to use military force against Mexico in response, and both the House and Senate vote to approve the use of force against Mexico.
• Approximately 6,500 Marines invade and occupy the city
• Shortly after military operations begin Wilson gets word of a ship about to dock at Veracruz that contains machine guns and munitions, which he fears will strengthen Huerta’s regime.
• Wilson thinks US troops will be greeted as liberators, but Mexican naval cadets and civilians start fighting US forces after Huerta’s forces pull back. Huerta’s opponents also denounce the US intervention, contrary to Wilson’s beliefs (sound familiar?)
• Source: CFR Page on the invasion of Veracruz

When and Why Does the US Use Force?

But what general factors should we think about?

Two broad categories:

• International factors

• Domestic factors

When and Why Does the US Use Force?

International factors

• Opportunities to use force

• Interests

  • Security Interests

  • Economic interests

• Specific details vary, but we can distill motivations down into some broad groupings
• Security interests would be things like destroying a rival’s capacity to launch an attack on the US, or thwarting an actual planned attack.
• Economist interests can include access to new markets, or access to natural resources

Predictors of US military intervention in civil and international crises

Predictor	Civil Wars	International Crises
Ally involvement	+	+
Rival intervenes first	+	+
Volume of trade
Relative power of target
Distance from US	+
Population of target	-
Democratic states
US growth rate
# Other states involved		-
Note:
Fordham, Benjamin O. 2008. Power or Plenty? Economic interests, security concerns, and American intervention. International Studies Quarterly. 51(1):737-758.

Notes: - Fordham (2008) analyzes cases where the US intervenes in international and internal/civil conflicts - Talk about coefficients

Notes

• Short run effect of trade on alliance formation

When and Why Does the US Use Force?

Resolve

• Politicians often talk about this a lot, but what is it?

A signal that an actor is willing to endure costs over a long period of time

• But how can actors effectively communicate resolve?

Notes

• Resolve is often something that politicians talk a lot about
• Cases like Trump’s cruise missile attacks on Syria are intended to demonstrate US resolve and signal the US’ seriousness about a particular policy issue
• Dr. Danielle Lupton has done work on this. She discusses the fact that things like cruise missile strikes are viewed as safe and effective means of signaling US intent and resolve, but the fact that they’re low cost undermines their effectiveness.

Vice President Mike Pence stares down North Korean soldiers from a parapet along the de-militarized zone. “I thought it was important that we went outside…I thought it was important that people on the other side of the DMZ see our resolve in my face.”

Notes

• Mike Pence famously walked up on to the parapet and said he wanted North Koreans to see the resolve on his face
• Lupton’s research suggests this kind of thing makes for a good photo op, but does little to actually communicate resolve or effectively signal intent to an adversary, particularly when earlier statements and actions undermine these later efforts.
• Lupton’s research also shows that leaders who fail to live up to their hawkish rhetoric face consequences. She notes that this stuff might play well domestically, but have consequences internationally.

When and Why Does the US Use Force?

Domestic Political Factors

• Diversionary use of force?

• Partisanship?

• Ideology?

Notes

• Various domestic factors can also matter
• But what are they?
  • Do leaders use force to distract from domestic problems?
  • Are the parties different?
  • Does ideology shape incentives to use military force?

When and Why Does the US Use Force?

Diversionary Use of Force

• The idea is to distract from poor economic or domestic political conditions

• Use of force triggers a “rally” effect, increases presidential approval/favorability ratings

Front page of the December 17, 1998 issue of the New York Times. President Bill Clinton ordered air strikes against targets in Iraq in the midst of an unfolding impeachment process.

Notes:

• It can be REALLY hard to escape damning domestic political events
• Using military force typically doesn’t create sustainable conditions that can help leaders distract from their problems.

When Does the US Use Force?

But diversion may be more complicated

• Parties are better/worse equipped to respond to “bad” conditions

• We can think of policy as substitutable, rather than strictly as diversionary

• Example: Unemployment

  • Democrats

  • Republicans

Notes - Diversion can be more complicated - Parties don’t face the same incentives, and don’t have the same cost-benefit calculus when looking at different policy options. - Democrats typically don’t have the same limits as Republicans when it comes to inflationary macroeconomic policy. They can respond to growing unemployment with stimulus spending more easily.

Figure 1 from Clark, Fordham, and Nordstrom (2011) showing the relationship between unemployment and US conflict behavior, broken down by president’s party.

When Does the US Use Force?

What about other countries?

• So far we’ve assumed the US initiates the use of force, but sometimes it’s also a target

• We often focus on decision-making within the US, ignoring the decisions of other states

• What sorts of factors determine when other countries target the US, and the intensity with which they do so?

When Does the US Use Force?

When is the US a target?

• A few factors to consider
  • When is a target vulnerable?
  • When is a target’s hands tied?
  • When do you want to avoid “poking the bear”?

Diversionary logic can help us here:

• Economic conditions: States try to avoid conflict with the US when economic conditions are bad (e.g. high unemployment).
• Partisanship: Prior beliefs about how likely presidents of different parties are to use military force may shape other states’ decisions about attacking the US.
• Rivalry: States with long-standing grievances and hostility towards the US may be more likely to use force in general.

Correlates of foreign conflict behavior towards the United States, 1946-1992

Outcome/Variable	Effect
Conflict Intensity
US conflict behavior	+
US Unemployment rate	-
Democratic president	+
Communist state	+
Variation in State Behavior
State power	+
Communist regime	+
Note:
Dave Clark, Ben Fordham, and Tim Nordstrom. 2011. Preying on the Misfortune of Others: When do states exploit their opponents' domestic troubles? Journal of Politics. 73(1):248-264.

Notes

• Focuses mostly on the Cold War period, so some of these effects may be more or less relevant today.

Constraints on the Use of Force

Constraints on the Use of Force

A puzzle:

• The US is the most powerful state in history, but it loses wars and we never see its military capabilities used in full. Why?

• What constraints exist on US military power?

• What are the limits of US military power?

Constraints on the Use of Force

Some key factors:

• Law and legitimacy

• Risks, costs, benefits

• Credibility

• Public support

• What will allies do?

• What will rivals do?

• Is the military the appropriate instrument of power for the goal in question?

Constraints on the Use of Force

Constitutional Authority

• The US Congress has had the authority to declare war (Article I. Section; 8. Clause 11)

• The President is designated by the Constitution as Commander-in-Chief of the US military (Article II. Section 2. Clause 1)

• Congress has also previously exercised the authority to delegate limited uses of military force, short of war

  • Example: Quasi-War with France, 1798-1801

• The Executive has claimed more authority and autonomy over time, particularly in the post-WWII era

Notes

• Presidents are Constitutionally designated as commander-in-chief of US military, but the Constitution doesn’t specify what their exact powers are.

• Quasi- War with France was a limited naval war with France and French privateers who were attacking US shipping in the Caribbean.

• In 1799 Congress authorized the Navy to inspect and seize US ships they suspected were bound or sailing to any French ports.

• Supreme Court case of Little v Barreme (1804) concerned the seizure of US ships sailing from French ports, not to. The Court upheld Congress’ authority to delegate limited uses of military force to the president and ruled that the military could not exceed that authority, and that the seizure was outside the scope of Congressional authorization.

• Later Supreme Court Cases ruled that the President has some limited autonomy and could use military force to protect. US individuals.

Constraints on the Use of Force

War Powers Resolution of 1973

• A response to the Vietnam War and concerns about executive overreach

• Passed in 1973 Over President Nixon’s veto

• Requires:

  • § 3: Regular consultations, “in every possible instance,” with Congress prior to deploying troops

  • § 4: Report to Congress within 48 hours of troop deployment explaining cause and justification for deployment. Also requires ongoing reports while troops are deployed.

  • § 5: Places a 60 day time limit on the deployment of US personnel, absent Congressional action.

  • § 5: Empowers Congress to end US military action by concurrent resolution

Notes

• Recent strikes by the US military against boats in the Caribbean and Pacific do not have a clear legal basis and Congressional leaders have not been briefed by the executive.

  • At least 57 people have been killed by such strikes in the fall of 2025. They are nominally focused on fighting narcotics trafficking.

  • Also violates international law (next slide) because even if they are traffickers there’s no clear or obvious threat to the US.

  • See BBC News article

• SEC. 3. The President in every possible instance shall consult with Congress before introducing United States Armed Forces into hostilities or into situations where imminent involvement in hostilities is clearly indicated by the circumstances, and after every such introduction shall consult regularly with the Congress until United States Armed Forces are no longer engaged in hostilities or have been removed from such situations.

• SEC. 4. (a) In the absence of a declaration of war, in any case in which United States Armed Forces are introduced into 1) hostilities or situations where imminent involvement in hostilities in indicated, 2) into the territory, airspace, or waters of a foreign nation while equipped for combat, or 3) in numbers which substantially enlarge the United States Armed Forces equipped for combat already located in a foreign nation, the President shall submit within 48 hours a report to the Speaker of the House and the President Pro Tempore of the Senate.

  • This report must cite the conditions that necessitated the introduction of US forces, and the legislative authority under which the introduction took place, and the estimated scope and duration of the hostilities.

  • Requires continuous reporting while troops are in harm’s way.

• Requires the President to terminate the use of force within 60 days from the submission of the report as dicated by SEC 4.1.

Constraints on the Use of Force

International Law

• The UN Charter generally prohibits the use of force, except in two cases:

  • Individual or Collective Self-defense (Article 51)

  • When authorized by the UN Security Council to maintain peace and stability (Chapter VII)

• Hague Conventions focus on means and methods of warfare

• Geneva Conventions and other treaties place limits on the conduct of warfare

• Various other treaties and agreements

  • Convention against torture and other cruel, inhuman, or degrading punishment of 1984
  • Biological Weapons Convention of 1975 (BWC)
  • Chemical Weapons Convention of 1993 (CWC)
  • Nuclear Non-Proliferation Treaty of 1970 (NPT)
  • Anti-Personnel Mine Ban Treaty of 1997 (Ottawa Convention)

Notes

• Basically all of Chapter 7 of the UN treaty lays out the escalatory measures that the Security Council can take to maintain or restore international peace and security. This can include, if other measures fail or are deemed insufficient, the use of military force.

• Hague Conventions: Early efforts to place limits on the conduct of warfare. Focus on things like the rights of soldiers, wearing visible symbols, carrying arms openly, etc. Also covers rights of prisoners of war, use of POW labor, etc.

• Four separate Geneva Convention agreements, dating to 1864, 1906, 1929, and 1949, plus three additional protocols (1977 and 2005) that lay out rules for the conduct of war.

  • Convention 1: Focuses on the conditions and treatment of wounded and sick soldiers and medical personnel who are not taking active part in hostilities. This convention prohibits torture.

  • Convention 2: Focuses on the conditions and treatment of wounded, sick, and shipwrecked military personnel at sea. Similar to Convention 1, this convention prohibits torture.

  • Convention 3: Updates previous conventions on the treatment of prisoners of war to better reflect the changing nature of war and standards of living.

  • Convention 4: Focuses on the protection of civilians during times of war. Prohibits torture and inhumane treatment of civilians.

• Geneva Protocols:

  • Different from the treaties.
  • 1925 Geneva Protocol bans the use of poison gasses or bacteriological weapons.

• Notably the use of tear gas is banned in combat under the Chemical Weapons Convention (CWC), but is not banned for use in domestic law enforcement, including riot control. The United States signed the CWC but registered a reservation stipulating that tear gas is not covered under the CWC.

US test of an atomic bomb on Bikini Atoll, July 1946. The picture shows the first of two bombs tested, named “Able”. The second bomb generated a radioactive mist that turned test ships in the vicinity into “radioactive stoves”. Extreme military power is often of very little practical use.

Notes

• Difference between early atomic weapons and newer hydrogen bombs concerned the difference between fusion and fission. Later weapons used fusion. Fusion weapons are much more powerful than fission weapons.

• Fusion bombs were 700 times more powerful than the bomb dropped on Hiroshima.

Information from Department of Energy Office of Scientific and Technical Information.

A photo of “Ivy”Mike”, the first thermonuclear (Hydrogen) bomb test. November 1, 1952. The test took place on Enewetak Atoll, a section of the US Marshall Islands.

Constraints on the Use of Force

Domestic public support

• Public support generally diminishes over time

• As a rule, the costs of war only grow over time

• Military force becomes increasingly political, leading to greater congressional involvement

• Conflict reveals information over time, and may reveal faulty assumptions from war’s beginning

Constraints on the Use of Force

What will allies do?

• Allied leaders may press for limits on the scope of conflict

• They might withhold capabilities

• They might limit mission types in which their troops can participate

• Allied publics might not support expanding the scope of conflict

US supply routes into Afghanistan, 2009.

Constraints on the Use of Force

What will rivals do?

• Rivals might greet US escalation with their own action

• Rivals may benefit from overly aggressive US action

• Rivals might also ramp up their efforts to counter US in other geographic/issue areas

Constraints on the Use of Force

Are there better options?

• The US has come rely more and more on the military to do a wide range of tasks

• But the military may not always be the best tool for the job

• The use of force often requires deploying other forms of power, influence, and expertise, but the military can’t generate comparable levels of expertise in all issue areas as compared to other agencies

• Efforts to build soft power may be undercut or offset by US military presence