Germany gets divided into 4 or 5 small kingdoms and loses plenty of territory: Alsace and Lorraine as well as the Rhineland are returned to France, while Schleswig and Holstein return to Denmark, East Prussia to Poland, etc. Bavaria elects a communist government while Prussia becomes increasingly authoritarian. The Ruhr industrializes faster, increasing disparity with agricultural states.
Belgium gets divided into 3 distinct language zones (Walloon, French and German-speaking).
France loses a chunk in its South-East to Italy. France loses Alsace and Lorraine to Germany. France's overseas colonies revert to local rule.
Arab pirates ravage the Med.
Th Netherlands gets divided into multiple provinces isolating Catholics in the South, Protestants in the western provinces and Frisland off on its own. Economic disparity increase as poor farmers get poorer while (citified) merchants grow richer.
Russia is devastated by its Communist Revolution. Because Bolsheviks never gain a clear advantage, White Russians (Czarists) dominate their traditional estates, while capitalists dominate new cities. Estonians, Karelians, Kazars, Uzbeks, Georgians, Chechnians, etc. minorities declare their independence and Kievian Russ loses most of the terrain it conquered over the preceding 500 years. Lack of a standardized rail gauge cripples long-range trade.
Italy losses the Tirol to Austria, Sicily to Arabs, etc. and reverts to the dozens of tiny kingdoms it had before Garibaldi (1848).
The U.K. fractures into separate British, Welsh, Irish and Scottish kingdoms after losing most of her overseas colonies.
The USA deteriorates into 7 distinct nations: New England, Mid-West, Cascadia, South-Western desert, Deep South, Alaska and rust-belt after losing most of her overseas possessions. Petty customs duties cripple continental trade.
Ainu regain control of Northern Japanese Islands, Okinowans re-gain self-rule while the home-islands revert to feudal estates ruled by feuding samurai. Korean pirates raid at will along the Japanese coast.
As the Ottoman Empire collapses, Turkey is reduced to the Anatolian Penninsula allowing most traders to by-pass traditional trade routes. Because Kamal Ataturk died during WW1, Turkish Muslims lack a unifying leader.
The Austro-Hungarian Empire collapses into two separate kingdoms: Austria and a separate kingdom ruled by Hungarians. Along the way, A-H loses trouble-some tribes in Bosnia-Herzegovina, Bulgaria, Dalmatia, Kosovo, etc. After losing the Dalmatian Coast, Austria loses access to shipping in the Mediterranean.
Switzerland loses Locarno to the Italians and its massive, agricultural Vallee to France. Several German-speaking cantons join Austria or Germany, reducing Switzerland to its original 5, German-speaking cantons. Bridges and railways fall into disrepair
Scandavian nations renew old blood feuds, raping and pillaging their way around the Baltic the same at that Vikings raided their neighbors a thousand years earlier.