Interventions in weakly institutionalized societies have been central to U.S. foreign policy. These have been amongst the most costly expenditures in the U.S. federal budget and may have important national security consequences. The United States has employed a variety of strategies aimed at defeating insurgents and building states capable of monopolizing violence, ranging from the top-down deployment of overwhelming firepower to bottom-up initiatives to win hearts and minds. Our research identifies the causal effects of key interventions employed during the Vietnam War by exploiting two distinct discontinuities in U.S. policy: one varies the intensity of a top-down approach—air strikes—and the other compares a top-down military force approach to a more bottom-up hearts and minds approach.
The U.S. intervened in Vietnam to prevent the spread of communism, and fostering a state that could provide a bulwark against communism after U.S. withdrawal was central to U.S. objectives. A state monopoly of violence is an equilibrium outcome that relies upon both the capabilities of the state apparatus and citizen compliance. Top-down approaches to foreign intervention emphasize gaining citizen compliance by making it costly for citizens to oppose the state, whereas bottom-up approaches aim to increase the benefits of supporting the state by providing public goods, economic aid, and political opportunities.
The military force approach is summed up by the Vietnam–era adage: “get the people by the balls and their hearts and minds will follow.” Air strikes were a key component, with the Air Force receiving more than half of wartime appropriations and dropping twice as many tons of explosives as was dropped during World War II. Leaflets warned citizens of “death from the sky” if they did not cooperate with the South Vietnamese government. One scholar wrote that air strikes could be used to establish social control and then modernization would organically follow; another argued that countering communism required “a ruthless projection to the peasantry that the central government intends to be the wave of the future.” According to one general “The solution in Vietnam is more bombs, more shells, more napalm.”
This contrasts with the approach of building bottom-up support, advocated in Vietnam by the U.S. Marine Corps: “a positive program of civil assistance must be conducted to eliminate the original cause of the resistance movement.” Advocates of this view argue that a top-down, coercion-oriented approach is ill-suited to gaining cooperation, as citizens have many ways to undermine a state they do not genuinely support, even without joining an armed rebellion. Moreover, when states try to impose a simplified order from above, their failure to understand local realities and tendency to disrupt them can lead the scheme to fail.
The United States utilized “quantitative resource allocation metrics” to an unprecedented extent in Vietnam, and our study exploits a newly-discovered algorithm component of U.S. bombing strategy that includes discontinuities useful for identifying causal effects. Declassified Air Force histories document that one of the factors used in allocating weekly planned bombing missions was hamlet security. A key algorithm combined data from 169 questions on security, political, and economic characteristics into a single hamlet security rating. The output ranged from 1 to 5 but was rounded to the nearest whole number before being printed from a mainframe computer.
Our study identifies the causal impacts of bombing by comparing places just below and above the rounding thresholds. Outcome data on security, local governance, civic engagement, and economics are drawn from armed forces administrative records, hamlet-level variables compiled by a military-civilian pacification agency, and South Vietnamese public opinion surveys. Hamlets near the thresholds are similar prior to score assignment, but following assignment those that fall just below the cutoffs are significantly more likely to be bombed. We find no evidence that the hamlet-level score was used systematically for other resource allocations, such as ground and naval troops. Placebo checks find no effects during a 1969 pilot, when the score was computed but not disseminated.
Our estimates document that the bombing of South Vietnamese population centers backfired, leading more Vietnamese to participate in Viet Cong (VC) military and political activities. An initial deterioration in security entered the next quarter’s security score, increasing the probability of future bombing. Specifically, moving from no strikes during the sample period—a relatively rare event—to the sample average increased the probability of a local VC guerrilla squad by 27 percentage points, relative to a sample mean of 0.38. It also increased the probability that the VC was active by 25 percentage points and increased the probability of a VC-initiated attack on local security forces, government officials, or civilians by 9 percentage points. Public opinion surveys and armed forces administrative data show similar patterns. We find limited evidence for spillovers across nearby areas or within VC administrative divisions; when present, they tend to go in the same direction as the main effects.
While U.S. intervention aimed to build a strong state that would provide a bulwark against communism after U.S. withdrawal, bombing instead weakened local government and non-communist civic society. Moving from no bombing to sample mean bombing reduced the probability that the village committee positions were filled by 21 percentage points and reduced the probability that the local government collected taxes by 25 percentage points. The village committee was responsible for providing public goods. Bombing also decreased access to primary school by 16 percentage points and reduced participation in civic organizations by 13 percentage points.
Interviews of VC prisoners and defectors provide a potential explanation for why bombing increased VC activity: grievances against the government—particularly in cases where a civilian family member was killed in U.S. or South Vietnamese attacks—were strong motivators for joining the VC. Civilian casualties and property damage are plausibly particularly harmful to the trust between government and citizens that underlies an effective social contract.
Our study also sheds light on how the top-down approach compares to a more bottom-up strategy by exploiting a difference between Military Corps Region I, commanded by the U.S. Marine Corps (USMC), and Military Corps Region II, commanded by the U.S. Army. The Marines emphasized providing security by embedding soldiers in communities and winning hearts and minds through development programs. In contrast, the Army relied on overwhelming firepower deployed through search-and-destroy raids.
Evidence points to the differences in counterinsurgency strategies as a particularly central
distinction between the Army and Marines, and comparisons of hamlets on either side of the corps boundary suggest potential pitfalls of the top-down approach that are consistent with the bombing results. Specifically, we document that public goods provision was higher on the USMC side of the boundary for relevant public goods. Moreover, hamlets just to the USMC side of the boundary were attacked less by the VC and were less likely to have a VC presence. Finally, public opinion data document that citizens in the USMC region reported more positive attitudes toward the United States and all levels of the South Vietnamese government. Pre-period VC attacks, other pre-characteristics, geography, urbanization, and soldier characteristics—including Armed Forces Qualifying Test scores—are all relatively balanced across the corps region boundary.
Understanding whether heavily top-down counterinsurgency strategies are likely to achieve their desired objectives remains policy relevant. The culture of the U.S. Armed Forces has changed only slowly since Vietnam. Moreover, while targeting has improved significantly, it remains imperfect. Insurgents have responded by embedding more tightly amongst civilians and it is widely accepted that heavy reliance on air power will lead to collateral damage. Additionally, politicians continue to advocate a top-down approach. Our estimates highlight ways in which an intensive focus on top-down strategies could pose challenges to achieving U.S. objectives, particularly when insurgents are embedded amongst civilians as they are in the Middle East today. They do not reveal whether a bottom-up approach is more effective at achieving U.S. objectives than refraining from intervention, a question that is beyond the scope of this paper.
This research brief is based on Melissa Dell and Pablo Querubin, “Nation Building Through Foreign Intervention: Evidence from Discontinuities in Military Strategies,” National Bureau of Economics Research Working Paper no. 22395, July 2016, http://www.nber.org/papers/w22395.