The world is more interconnected than it's ever been.
The Iran war affected us all due to Hormuz.
The Yemen war affects us all due to the threat to Red Sea shipping.
The ongoing civil war in Sudan affects us too, given the huge numbers of people involved and the potential for refugee flows. The conflicts across Mali and the Sahel, likewise. ISIS and their ilk are not going to stop if they defeat the governments of those countries. They still hate the West just as much as they ever did.
Russia despises us. They hate European unity, democracy, the whole thing. They will not stop at Ukraine.
In case you weren't paying attention, in the 1930s the western powers tried to appease Hitler. They let him take Chekoslovakia. Did that stop him, or encourage him to keep going?
Did Chechnya satisfy the Russians who want to bring back the USSR? No, today it's Ukraine.
They will keep going until they are stopped.