sometimes vectors come together for a brief Golden Age

https://en.wikipedia.org/wiki/Second_International

The Second International (S.I.) was extremely dynamic. Its growth was an historic phenomenon. Almost every one of its associated national parties grew into significant political forces … even the one in the United States — Eugene Debs got 6% of the vote for president in 1912. The Socialist Party of America elected two US Congressional representatives, dozens of state legislators, more than 100 mayors, and countless lesser officials. Its weekly newspaper, Appeal to Reason, was subscribed to by half a million people in 1910, making it the largest-circulation socialist newspaper in American history and one of the most widely read periodicals of its time.

Over the two decades of the 1890s and 1900s all seemed propitious for the parties of the Second International. They had great authority and workers all over the world were singing The Internationale. Then World War I started in 1914, there was a Bolshevik coup in Russia in 1917, and the Marxist theory that had been the glue of the S.I. shredded. The world of revolutionary leftism got murky after that point — and has been ever since.