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,
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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
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
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.