It is kind of ironic that we've gotta defend Ukraine's borders but not ours.
In all the territories taken back by Ukraine hundreds of local "collaborators" were prosecuted and charged with terrorism and they'll get 25 years. The 50,000 people working for Donetsk city government and the 110,000 in the militias all face terrorism charges if they surrender. So they won't surrender. And if Putin handed them over, his own people would lynch him. So, until Ukraine gives up on trying to take back those ethnic Russian regions (and prosecute the tens of thousands of "collaborators") they'll keep fighting.
Ukraine is buying a lot of mercs from South America now.