I wouldn't say it was just that. The Ukrainians realized they were in trouble in 2014 when Russia lopped off Crimea, and ordered a painful introspective to high

I wouldn't say it was just that. The Ukrainians realized they were in trouble in 2014 when Russia lopped off Crimea, and ordered a painful introspective to highlight all the weaknesses of their military. They spent 8 years overhauling their military and learning from invited western forces to prepare for an invasion that they hoping beyond all would never come. And it paid off in spades.