The Renaissance started in Italy for many different reasons. For one, the Italians simply saw what they used to be... the ancient city of Rome, mainly. They also probably wanted stability, with all this war and church nonsense going around. Finally, they needed something to do in these dark times, I would imagine.
Rome was a magnificent city, and it flourished with life and prosperity... unlike the Italy prior to the Renaissance. I believe Rome's ruins was a prime factor in the Renaissance; I, personally would feel very motivated to create new cities and artwork by seeing what we as a country used to be. To me, it's as if the ghosts of their magnificent past came back and told them to get their act in gear, and they listened.
With the Holy Roman Empire and all this church rubble going around, I'm sure the Italians wanted stability and comfort.
English: Map of the Holy Roman Empire in the 10th ...
Renaissance Faire 2012
Renaissance violComfort is very much so in the mind of the beholder, and I suppose artwork and innovation was comfortable to them in those times of war. Staring at the beautiful artwork of Michelangelo would definitely motivate me, personally.
Finally, the Italians needed something. Something to entertain them, to take their minds off their misery or poor governmental conditions. Art is a very calming thing, and I'm sure many found peace in doing so. The Renaissance was a must, and it happened.
So, in conclusion, the Renaissance happened in Italy for three main reasons; they saw what they used to be, wanted stability, and wanted an escapement from reality. The Renaissance was a great period and some of the best artwork ever created by mankind has come from it, too.