The US wants a war with Russia without putting boots on the ground. Ukraine was a convieinient excuse.
9/11 triggered a war with random middle eastern countries that the US wanted to invade anyway.
If Cuba downed a large cargo ship, then the US will have annexed it before midnight. If China downs one in South China sea, the US might keep it quiet because neither country wants a violent escalation into war just yet.
War is premeditated. The inciting event is just the excuse.