The Russian president Putin is using this war against the good people of Ukraine to bow to his plan and that they should not even think of joining NATO.
This is one reason, apart from this Putin wants to form the Soviet Russia which is the union of countries and be more powerful as the past. For now Ukraine looks like a hindrance as they weren't obeying the orders. This has happened after the new President Volodymyr Zelenskyy took rule of Ukraine. If he had behaved as a puppet as the previous president Petro Poroshenko now this couldn't have happened.