A starting point for modern history is when steam power starts to take over from muscle power & wind power which means circa 1814.
George Stephenson, an Englishman brought us the first practical steam locomotives and railways. His first engine ran in 1814. The most famous is the Rocket, a railway engine which hauled people or coal in 1829. This was a landmark in the Industrial Revolution which the Wikipedia puts from 1750 to 1850. It was a revolution with consequences, winners and losers. One reaction was Socialism.
The early socialist movement came from decent men who cared about the down trodden. The Wikipedia refers to it as Utopian socialism, putting its period to 1800 - 1825. They were looked down on for being reactionary. The revolutionaries were driven by hate. Karl Marx started as a Utopian but changed to the hatred we see in the Communist Manifesto. It is not just Workers of the world, Unite! It was a lust for mass murder:-
In short, the Communists everywhere support every revolutionary movement against the existing social and political order of things.
The Communists disdain to conceal their views and aims. They openly declare that their ends can be attained only by the forcible overthrow of all existing social conditions. Let the ruling classes tremble at a Communistic revolution. The proletarians have nothing to lose but their chains. They have a world to win.
The whole thing was roughed out by Marx and Engels in the Red Lion in Great Windmill Street where, in November 1847 the Communist League held their second congress in a room above the bar. It was a bit like that Last Supper in an upper room. Something on the background is at the Communist League published by the Marx/Engels Archive.
In 1891 there was another landmark, Rerum Novarum, a letter to the bishops and the faithful written by Pope Leo XIII. He said that Capitalism is bad but Socialism is worse. The Russian Revolution which led to some 85 million deaths [ See The Black Book of Communism ] proved that Leo was right about socialism.
The Russian Revolutions in 1917 led on to others:-
German Revolutions
Bavarian Soviet Republic
Hungarian Soviet Republic
The March 1921 Action [ Marzaktion ] Germany March 1921
armed actions of the proletariat which had begun with the struggles in Berlin in January 1919
Spartakus
White Rights
Communist attacks in Germany