The purpose of modern political movements

What is the purpose of modern political movements. No, what IS a modern political movement? (MPM) I wonder what happened to the times where political movement meant business. Like when there was a political movement SO DANGEROUS that it would threaten the stability of a system. I fail too see a political movement of this power. Because what, communism? Like for real? What is radical about communism to current youth? Current youth doesn't give a fuck about communism. So what constitutes a modern political movement? It must be completly grassroots that's for sure.