Ukraine's leadership is proving to be the "most important difference right now" between Russians and Ukrainians in the war, according to Gen. Mark Milley.

The Joint Chiefs chairman detailed to the Senate Appropriations Subcommittee on Defense on Tuesday, where he testified with Defense Secretary Lloyd Austin, why he believed Ukraine's resistance has been so successful, specifically in keeping the Russians away from Kyiv, Ukraine's capital, and Kharkiv, Ukraine's second-largest city.

“In terms of lessons learned, leadership is clearly the key from [Ukrainian President Volodymyr] Zelensky all down to the lowest private,” he said, adding, "They are capable. ... Probably the most important difference right now between the Russians and Ukrainians is the leadership throughout the levels.”

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Milley then pointed to the training that the Ukrainian military has received since 2014 as a key contributing factor to its success.

“In addition to that is what the western nations, NATO, in particular the United States, taught their leaders since 2014 about mission command," the chairman continued. "The Ukrainians are practicing a decentralized intent-based set of tactics. The Russians are practicing a top-down, very, very top-heavy directive in nature. [A] sort of set orders come in from the top, which is not necessarily the best thing to do in a dynamic battlefield."

The United States had roughly 160 members of the Florida National Guard in Ukraine executing a train-and-advise mission to develop the Ukrainian Armed Forces’ Combat Training Center in Yavoriv since 2015, though Austin pulled them out before Russia invaded. Many of those U.S. troops are now training Ukrainian soldiers on weapons, including howitzers, that the U.S. and other countries have provided.

"The recent reunion now with these Florida National Guard members with their Ukrainian colleagues, we are told, was an emotional meeting given the strong bonds that were formed as they were living and working together before temporarily parting ways in February," Pentagon spokesman John Kirby said last week. "This new training effort in Germany and other locations in Europe is in direct support of recent U.S. security assistance packages that are designed to help Ukraine win their battles today and build strength for tomorrow."

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Milley also acknowledged the use of the weapons from the U.S. and other countries as a factor contributing to Ukraine's success.

"The second thing is the effective use of anti-tank weapons has been phenomenal on the part of the Ukrainians. A third is the denial of the airspace, air superiority," he said.