It's not terrain you ever want to be invading through, though. Check out the "winter war". Invading would be a crapshoot both ways. The Ukrainian border has n

It's not terrain you ever want to be invading through, though. Check out the "winter war". Invading would be a crapshoot both ways. The Ukrainian border has no geographic features that would impede an invasion though, and would let NATO cut Russia off from its oil fields, form a land bridge to the caspian sea and cut Russia off from the black sea entirely all within about a day. Its strategic significance cant be underestimated.