What is ascension? Is that when you finish all levels and start over?

Yes, ascension is resetting all the levels so you start at the beginning with the full AP amount available. Up until a few hours ago you needed to finish all levels; now you just need to finish Europe Huge (so skipping levels can get you to ascension earlier) but you have to spend 100 AP to ascend. Since levels are designed to give about the same number of AP per time spent, skipping levels to ascend faster seems like a losing proposition to me, but the option is there.