When does a war reach a turning point? History supplies some answers.

In assessing whether the United States should continue to support Ukraine at current (or even expanded) levels in its fight against Russian aggression, many members of Congress are asking an understandable question: How much longer should we do this? Or, to paraphrase retired General David Petraeus from another conflict, the Iraq War: “Tell me how this ends.”

There is of course no easy answer to this question. War is almost always unpredictable in its course of events, cost, duration and outcome. But with the all-out war in Ukraine now 19 months old, we should probably view it, tragically, as still a fairly young conflict. The history of wars fought by the United States, a country with a solid military record yet also a nation that has often struggled in the early years of its armed conflicts, may provide some useful perspective. 

America’s wars are not Ukraine’s, and they are not all similar to each other. But a survey of major American wars over the centuries suggests that major conflicts often reach their key turning points somewhere between two and three years into the struggle.

Let’s start at the beginning. After early successes near Boston in 1775, American patriots faced adversity from the Battle of New York onward. The Revolutionary War went badly for the young United States throughout 1776 and beyond, even if George Washington successfully crossed the Delaware on Christmas night and scored some tactical victories in the following days, into early 1777. Not until the Battle of Saratoga in the early fall of 1777, though, can one identify with hindsight that a crucial turning point had been reached. French support for the U.S. followed in 1778; the decisive Yorktown victory occurred in 1781. Thus, the turning point, such as it was, took place about 29 months into the war.

In the War of 1812, after much fighting along the U.S.-Canada border that went back and forth early in the war, the British burned down key federal buildings in Washington in the late summer of 1814. But they were stymied at Fort McHenry in Baltimore in September, where Francis Scott Key was inspired to write “The Star-Spangled Banner”; the United States thus finally arrested British momentum about 27 months into the conflict — as clear a turning point as one can probably identify for that ultimately stalemated war.

In the American Civil War, the Confederacy more than held its own for the first two years of conflict, but with the crucial Union victories at Vicksburg and Gettysburg, both in the early days of July 1863, momentum definitively shifted. The war was far from over, but the South was thereafter always on its back foot. Thus, the military turning point was about 27 months into that struggle as well.

World War I and World War II are more complicated, since many parties were involved, and America entered each conflict belatedly (after supplying allies with weapons for years prior to its actual combat involvement, in both cases).

In WWI, the United States declared war in the spring of 1917. But Germany was still on a roll through that year against Russia, as the Tsar’s regime collapsed, and then on the western front of Europe in early 1918. Not until the late summer of 1918, at Saint-Mihiel, France, and elsewhere, did the arrival of U.S. forces en masse reverse Germany’s momentum. So the turning point was about 17 months after America’s entry into the war, and four years after the war’s overall start in August of 1914.

In World War II, the tide shifted by late 1942 in the Pacific, by early/mid 1943 in the “Battle of the Atlantic,” and by the summer of 1943 in Sicily. Relative to America’s entry into the conflict in late 1941, the turning points happened 12 to 20 months into the war — but more like three to four years after the initial German invasion of its neighbors in Europe.

In Korea, after back-and-forths through 1950 and early 1951, General Matthew Ridgway finally helped stabilize the front about a year into the war. Fighting then continued, and stalemate ensued, for two more years. The turning point, such as it was, occurred after about 10 to 12 months — but it was not a decisive turning point.

In Vietnam and perhaps Afghanistan, there never was a clear and definitive change of momentum in favor of the United States and its partners. In Iraq, the successful surge occurred four years after the overthrow of Saddam, with clear results apparent by the summer of 2007 or about 50 to 52 months into the war.

Past is never exact prologue, and Ukraine’s military experiences may not mirror America’s, of course. But as a set of historical cases that may tell us something about the nature of modern war, America’s experience with its own conflicts suggests that 20 months of fighting is, alas, not very long. Most often, it takes two to three years for the winning side to gin up enough military production, mobilize enough forces, develop innovative tactical as well as operational concepts and apply those ideas on the battlefield long enough to turn the tide.

Ukraine has only had high-end armored weapons for a few months, and is still awaiting substantial numbers of modern combat aircraft as well as longer-range missiles. Those facts, combined with historical perspective on how long even successful wars usually last, suggest that it makes sense to give Ukrainian forces at least another year of trying to liberate their territory and protect their people before we conclude that a backup plan is needed.

Michael O’Hanlon is the Philip Knight Chair in Defense and Strategy, Brookings Institution, and author of “Military History for the Modern Strategist: America’s Major Wars Since 1861.”