Most of the nations apart from Baltic states are Pro Russian.
Maybe u need to know the following .Ukraine was a state created by Lenin/Bolsheviks after Russian Revolution in 1917. After winning World War 2 some parts of Poland were added to Ukraine by U.S.S.R. The adding of land came with Poles . Now Poles since time memorial have been having problems with Russians although they are the same tribe/race called Slavs.
Prior to the Genocide which started in 2014 Majority in Ukraine were Russian Speaking Citizens living in the East . Most moved to Russia to escape the war instigated by Kiev and the balance changed with the Western Ukrainians(Polish Ukrainians) becoming majority.
When Latvia , Estonia , Lituania joined NATO Putin was too much preoccupied in restoring Russias economy that he closed his eyes when Russians en mass were relocating back to Russia. With NATO on their side the Baltic Countiries banned use of Russian language and stopped employment of Russians in Government offices. It was so bad that they had language polices. Majority of Russians ressetled back to Russia primarily in St Petersbourg.
Putin put a redline of Natos expansion with Ukraine. Biden thought he was smarter than in 2014 refused to sit down with Putin and listen to him. The outcome is this a single mistake and we have a nuclear war.
What if people from former soviet union join to protect Ukraine?
Because they see themselves as next if they do nothing.