Ukraine isn’t “defending itself from an invasion”. Ukraine’s democratically elected government was overthrown by a US sponsored military coup. The coup was carried out by Nazis that want to ethnically cleanse ethnic Russians from the territory. The Russian majority areas voted overwhelmingly to secede from Ukraine and called on Russia to protect them when the Ukrainian coup government invaded them.

Russia’s goal is not “conquering all of Ukraine”. Russia’s military objectives are

1. Halting the ongoing killing of ethnic Russians in the Donbas Republics by the Ukrainian nazi coup government.

2. Disabling the nazi coup government’s military capacity to act as a staging ground for US attacks on Russia.

Russia has continually offered ceasefires with the only substantive condition being “stop killing Russians”, and the nazi coup government has been unwilling to negotiate because the US has told them they’re not permitted to stop killing.