With global sanctions going on the only life blood that is left for Putin and Russia is its oil. If we stop buying oil from Russia this will stop providing Russia with the resources needed to fund the war that they are currently taking to Ukraine. 

The other big thing to remember that Putin will most likely not stop with Ukraine and probably expand to other countries near by. If the nations don't band together and stop the purchases of Oil from Russia and allow them to continue to occupy more of Ukraine there will be many long term issues for everyone around the world.