What History Tells Us About Abandoning Strategic Allies

In the study of international relations, few decisions carry consequences as far-reaching as the abandonment of a strategic ally. The immediate costs are visible — a nation falls, a population suffers. But the second- and third-order effects are where the real damage accumulates: alliance networks fray, adversaries recalculate, and the entire architecture of regional stability shifts.

Three historical cases — separated by decades and continents — reveal a remarkably consistent pattern.

Czechoslovakia, 1938: The Price of "Peace in Our Time"

When Britain and France signed the Munich Agreement in September 1938, they believed they were purchasing peace by ceding Czechoslovakia's Sudetenland to Nazi Germany. The logic seemed sound: a small territorial concession to avoid a catastrophic war.

The consequences were anything but peaceful:

• Six months later, Germany occupied the rest of Czechoslovakia — demonstrating that the concession had satisfied nothing
• The Soviet Union, observing that Western democracies would not fight for their allies, signed the Molotov-Ribbentrop Pact with Germany — directly enabling the invasion of Poland
• Smaller European states lost faith in collective security guarantees, with several pivoting toward accommodation with Germany
• World War II began eleven months after Munich, at far greater cost than early resistance would have entailed

Historians have extensively debated whether war in 1938 would have been winnable. What is not debated is that Munich accelerated the very conflict it was meant to prevent. The Czech army — 35 well-equipped divisions behind strong fortifications — was eliminated as a factor without firing a shot. Germany gained the Škoda arms works, one of Europe's largest weapons manufacturers, and the strategic confidence to push further.

As Churchill observed: "You were given the choice between war and dishonour. You chose dishonour and you will have war."

South Vietnam, 1975: When Credibility Collapses

The fall of Saigon in April 1975 was the culmination of a gradual American withdrawal — not a sudden decision, but a slow erosion of commitment that allies and adversaries alike watched carefully.

The Paris Peace Accords of 1973 included American assurances that the United States would respond to major North Vietnamese violations. When those violations came — in the form of a full-scale conventional invasion — Congress blocked military action and cut aid. South Vietnam, deprived of the air support and materiel it had been structured to depend upon, collapsed in 55 days.

The strategic aftershocks were substantial:

• Southeast Asian dominoes partially fell. Laos and Cambodia fell to communist forces within weeks. Thailand, Malaysia, and Indonesia accelerated hedging strategies.
• Soviet confidence surged. Moscow expanded its involvement in Angola, Ethiopia, Afghanistan, and Central America throughout the late 1970s — a period historians term the "arc of crisis."
• Allied confidence cratered. A 1975 State Department survey of allied governments found widespread doubt about American reliability. Japan, in particular, initiated quiet reassessments of its security posture.
• The "Vietnam syndrome" constrained American foreign policy for over a decade, creating power vacuums that adversaries exploited.

The financial calculus is instructive. The United States spent approximately $850 billion (2024 dollars) on the Vietnam War over two decades. The cost of sustaining South Vietnam's military with adequate arms and air support would have been a fraction of that figure — but by 1975, the political will to spend even that fraction had evaporated.

Afghanistan, 2021: The Speed of Collapse

The withdrawal from Afghanistan provides the most recent — and in some ways most instructive — case study. After 20 years, $2.3 trillion in expenditure, and the construction of a 300,000-strong Afghan National Army, the United States withdrew. The Afghan government collapsed in 11 days.

The speed of the collapse is itself the critical data point. The Afghan military, built to operate with American air support, intelligence, and logistics, could not function independently. When those capabilities were withdrawn, the entire structure disintegrated — not because Afghan soldiers lacked courage, but because the system was designed around a commitment that was revoked.

The global response was telling:

• Taiwan's Ministry of National Defense publicly stated that the fall of Kabul reinforced the need for self-reliance, while privately expressing concern about American commitment — a dynamic reported by multiple credible outlets including Reuters and the Financial Times.
• Japan and Australia accelerated defense spending increases and deepened bilateral security cooperation, hedging against the possibility of reduced American reliability.
• China's state media broadcast the Kabul imagery extensively, with explicit messaging directed at Taiwan: "This is what American promises are worth."
• European NATO allies, who had deployed forces alongside the US in Afghanistan, found their own populations questioning the value of alliance commitments.

The Pattern: Three Consistent Dynamics

Across these three cases, separated by decades and vastly different circumstances, three dynamics repeat with striking consistency:

1. Adversaries expand. In every case, the power that benefited from abandonment did not stop. Germany took all of Czechoslovakia, then Poland. North Vietnam absorbed the South, and communist forces advanced in Laos and Cambodia. The Taliban immediately consolidated control and expanded ties with allied militant groups. Accommodation does not satiate — it encourages.

2. Allies hedge. When a security guarantee proves unreliable, rational actors diversify. After Munich, Eastern European states accommodated Germany. After Vietnam, Asian allies began independent defense buildups. After Afghanistan, the Indo-Pacific saw accelerated multilateral security arrangements (AUKUS, expanded Quad cooperation) — essentially allies building insurance against the possibility that American commitments might again prove hollow.

3. The cost of the next crisis increases. This is perhaps the most important and least intuitive finding. Abandoning an ally does not save resources — it spends them, by creating a more dangerous strategic environment that requires greater expenditure to manage. The cost of World War II dwarfed what defending Czechoslovakia would have required. The "arc of crisis" after Vietnam consumed far more American resources than sustaining South Vietnam would have. The strategic consequences of Afghanistan continue to compound.

The Current Test Case

Today, the international community faces a situation that maps onto this historical pattern with uncomfortable precision. In the Western Pacific, a democratic society of 23 million people — deeply integrated into the global economy and hosting the world's most critical semiconductor manufacturing — exists under growing military pressure from a neighboring great power.

The parallels are not exact — they never are. Taiwan's economic importance vastly exceeds that of any previous case. Its semiconductor industry represents a concentration of strategic value without modern precedent. The military balance in the Western Pacific is more complex than any of the historical examples discussed. And the nuclear dimension adds a layer of risk that 1938, 1975, and 2021 did not share.

But the underlying dynamics — credibility, deterrence, adversary calculation — operate on the same principles. A RAND Corporation study published in 2024 found that allied confidence in American security commitments correlates directly with defense spending patterns and alignment choices across the Indo-Pacific. When confidence drops, allies either arm independently (increasing instability) or accommodate the regional power (shifting the balance further).

The Center for Strategic and International Studies (CSIS) wargame series, conducted between 2022 and 2025, consistently found that the single most decisive variable in Western Pacific conflict scenarios was not any weapons system, but the speed and credibility of allied response. Scenarios where allies acted quickly and cohesively produced dramatically different outcomes from those where commitment was ambiguous.

The Arithmetic of Credibility

Deterrence theorists describe credibility as a "wasting asset" — it depletes with each failure to act and can only be rebuilt slowly and at great cost. Thomas Schelling's foundational work on the subject demonstrated that the cost of maintaining a commitment is almost always lower than the cost of rebuilding credibility after abandoning one.

The numbers bear this out. Post-Vietnam, the United States spent heavily on the Reagan-era defense buildup partly to restore credibility damaged by the fall of Saigon. Post-Afghanistan, the AUKUS submarine deal and expanded Pacific force posture represent hundreds of billions in new investment driven substantially by the need to reassure allies.

The pattern suggests a simple, if uncomfortable, conclusion: the question is never whether to pay, but when — and at what price. History has been consistent in its answer. Paying early, through sustained commitment, costs less than paying later, after credibility has been spent.

The data is there for anyone willing to look at it.

Further Reading

• Why Taiwan Matters to the Entire World — Not Just Asia
• What Ukraine's Defense Taught the World About Deterrence
• 5 Realistic China-Taiwan Invasion Scenarios for 2026