Easy.
Germany heads east in 1914 instead of west, avoiding the invasion of Belgium and not involving itself in USW. With Russia set to fall by the end of 1915, Britain enters the war to keep France from having to make a negotiated peace. Italy sides with Allies and offensives in the Alps and Alsace-Lorraine begin. Austria-Hungary starts to fall to the Italian-British force and Germany is forced to shore up their line. But Russia capitulates with a Republican revolution in 1916 with Lenin being executed by the President of Russia, Alexander Kerensky. When Germany moves its attention west, it plows through Belgium but the offensive peters out after taking Paris. Italy has kept its gains on Austria. After a few months of Paris and most of northern France being occupied, Germany pushes on another offensive to seize the rest of Normandy and Brittany. With the 1917 offensive looking likely to succeed and cut off British aid, the Entente sue for peace, with Germany acquiring some token border towns, French Central Africa and Congo, and the Belgian Congo. Old Willy rejects any peace, demanding a border on the Meuse, dismantling of arms industry, and heavy reparations from Britain, who remains undefeated at sea and has their Expeditionary Force intact. After a few weeks of American mediation, Willy refuses to budge and attempts to dismiss Zimmerman, who has been pushing for a more lenient peace, due to fears of American intervention and a possible renewed war with Russia. Hindenburg detains the Kaiser and sends him into seclusion then asks the Reichstag to vote upon a peace treaty with the Entente(bypassing the Bundesrat) that he, Ludendorff, and Zimmerman negotiated. This treaty is similar to the terms asked for by Britain and France, but with limits to the size of the French and Italian armies, dismantlement of French and Italian war industry, and arrangements for a naval conference in Washington DC. Austrian-Italian border is status quo antebellum.
The vote passes, and further votes arrange an amended Constitution not unlike the October Constitution of OTL. With the integration of Germany into the world order and increased democratization, Germany looks poised to be the capitalist democratic power of the mid-20th century.
With Russia having surrendered without Russia proper being occupied and without the Tsar's permission, Russia develops a stab-in-the-back theory, with Jews and Communists, usually Jew Communists like Trotsky, being the bogeyman that made Russia fall. During this time, there is great strife, with pro-Tsar forces and Republican forces and Communists clashing in the streets and new fascist forces claiming a need for the Russian nation to stand united against outside influences and impurities. In 1923, a lieutenant general named Baron von Ungern-Sternberg marches on the Taurida Palace with what he said was 50,000 blackshirts (history points to more like 4,000 blackshirts and a large pro-Tsar mob of about 15,000) with demands to reinstate the Tsar as Emperor, expel all Jew- and Socialist-sympathizing deputies from the Duma, and proclaim Baron von Ungern to be Protector of Russia, with emergency powers to end the strife that's been causing great economic distress and to restore order to Ukraine, which had fallen into anarchy. The Duma voted unanimously.
America fell into a depression immediately after the war. The stock market crashed. All the factories selling shells to the French closed down, some banks that had lent to the British and French in hopes of them winning the war went broke. This led to bank runs all across America, with millions taking their savings home with them. Further exacerbating manners is the rise of the KKK and worsening race relations. Seeing the potential for action in such circumstances, the IWW (which was not broken up and leaders deported thanks to no passing of the Espionage Act) reunited with Daniel DeLeon and his Detroit IWW. With membership pushed up by infamous acts such as the Seattle General Strike and the March on Millionaires, the Industrial Workers of the World started building its own factories and tenements with member dues. This caused major crackdowns in Chicago, where National Guard units were called in by the Governor to evict the Wobblies who had fought off city police. This led to the burning of a tenement by the National Guard in which 127 people died, mainly women and children. With the Massacre of Chicago on everyone's mind, Eugene Debs officially joined the IWW and endorsed its platform of Syndicalism.
Enter 1924: six years into depression and strife, Eugene Debs and Daniel DeLeon run a joint ticket on the newly-formed US Labor Party. With an explicitly socialist agenda, the Labor party starts sweeping local elections, grabbing cities like Seattle and Pittsburgh and forming city Labor Syndicates to organize municipal economies. Some state legislatures even attain what would be a Labor plurality, if the Democrats and Republicans didn't enter into coalition whenever Labor tried to do anything. The election is a fiery one, with tours across the United States and coercion for votes on all three sides. When the vote for President finally comes in, the Electoral College votes 308 for Calvin Coolidge(R), 160 for John Davis(D), and 63 for Eugene Debs(L). Americans are outraged, as the popular vote put 11,832,202(40.8%) votes for Debs, 10,399,567(35.9%) for Coolidge, and 6,709,968(23.1%) for Davis. This meant that the President-Elect had lost the popular vote by almost five percent but won the Presidency by a landslide.
To socialists around America it only confirmed their worst fears, that America was not a democracy at all, but rigged for the establishment parties by the rich. Debs tried to rally his party around the 1926 election, but was soon voted out as head of the party by none other than his own running-mate Daniel DeLeon, who advocated a march on the Capitol building to confirm Debs' nomination as President. The march, organized by the Labor party and supplied by IWW Syndicate cities from around the country. Almost 100,000 people showed up to march on Congress, but the US Army First Infantry Division and the Regiment of Dragoons we encamped at the National Mall and ordered the crowd to disperse and cease "any and all seditious activity against the United States Government." This only emboldened the protesters, as many were armed with rifles and bombs. It's not known who fired first, but by the end of the day 2,000 protesters and 300 soldiers were dead, Washington was in flames, and the Second American Civil War had begun, and Union of Socialist Syndicates would rise in its wake.