The war in Ukraine has entered a new, and more difficult, phase | Daniel R DePetris and Rajan Menon

Ukraine is struggling on the battlefield - and its western allies are grappling with economic and political trends that may weaken their support

Wars are a series of twists and turns. Momentum can shift and quickly alter fortunes on the battlefield, and intangible elements like leadership and motivation can shred the assessments of the most seasoned military analysts. Military campaigns that look promising initially can, over time, turn into quagmire, as mistakes accumulate, terrain changes and the adversary alters its tactics. The war in Ukraine is a textbook case in point.

During the war's first two months, the Ukrainian army proved to be formidable, courageous and highly innovative against a better-armed Russian foe, which military experts had almost unanimously expected would prevail. A day after Russia's invasion began, the US intelligence community was concerned that Russian forces would capture Kyiv in a matter of days. Vladimir Putin probably assumed a quick and relatively painless operation.

Daniel R DePetris is a foreign affairs columnist for Newsweek and a fellow at Defense Priorities, a thinktank that advocates for restraint in foreign interventions.

Rajan Menon is director of the Grand Strategy Program at Defense Priorities, senior research fellow at the Saltzman Institute of War and Peace Studies at Columbia, and non-resident scholar at the Carnegie Endowment for International Peace. He is the coauthor of Conflict in Ukraine: The Unwinding of the Post-Cold War Order