After the Second French Civil War 1764-67, many people in Europe were discussing the possibilities of republican / democratic experiments, until then only existing in smaller states. Traditional moarchists felt threatened by this development.
1768: After the death of the more cool-headed kings Humphrey III and IV of Britain and Héctor II of Spain, who were self-assured enough not to be impressed by the king-less situation of France, diplomatic tensions to France rapidly worsen. The first French Republican War begins. Savoy, the Netherlands, even Hungary under hesitating Charles VI and many German states join the coalition; only Italy stays neutral.
1768, September: Battle of Verdun. German armies defeat French.
1769: France orders the "levee en masse", creating the republican armies.
The pope flees from Avignon, first down the Rhone river to Corse, but later moves his seat to Toledo, Spain, since Italy still doesn't want to enter the war. In Spain, he outspeaks decidedly against republicanism, further encouraging the "monarchist crusade" feeling among the reigning classes in Europe. There are some hopes among conservatives that this may bring the national churches closer together and give the pope more power.
1769, April: British troops land in Aquitaine, to unite with the Spaniards.
1769, May: Battle of Aix-en-Provence - "the blackest day for the house of Savoy": Crown prince Filiberto is captured by the French, his brother Filippo and their cousin (also named Filippo) die in battle.
1769, August: Battle of Belfort. French kick out German troops from French soil. However, the Swiss Confederation now enters the war against France.
1770, March: Battle of De Panne. French defeat Dutch, who complain that the Brits didn't support them.
1770, July: British-Spanish army defeated before Limoges. Spain retreats from France, fights defensively.
1770, September: Battle of Pont-a-Mousson. German-Swiss-Hungarian troops defeated by French.
1771, February: Spaniards fight off French attack against the Pyrenees.
1771, July: Battle of Saarbrücken. French occupy SW Germany between Mosel and Rhine rivers.
1771, November: French Royalists in Algeria attempt a landing, supported by the Spanish navy, in South France. The landing itself is successful, but the people don't rise against the republic, and the landed troops are defeated. Many ships have to be abandoned.
1772, January: After the French used the holidays to move their armies, while the Spaniards were celebrating, Catalonia is overrun by the French.
1772, April: Battle of Maasmechelen. Last German-Dutch army defeated.
1772: Peace of Brussels. All the German lands west of the Rhine are annexed by France, plus the lands of Berg and Baden at the right bank. So are Spain north of the Ebro, French-speaking Switzerland, the Alsace, (old) Savoy and Nice. Switzerland is neutralized again.
Late 1770s: After the downfall of the French Indochinese Compagnie, France is struck by a severe financial crisis. General Boulanger takes "temporal power" (which has to be accepted by plebiscites once per five years).
War between republican France and the British-Spanish-German-Polish-Hungarian-Danish-Swedish coalition breaks out again in 1779.
1780: War starts promising for the coalition when the Spaniards retake Catalonia and the German-British-Dutch armies cross the Rhine and invade the Palatinate.
1781: Tide of war turns again for France, when Boulanger defeats the coalition armies at Worms (June) and Weissenburg (September) and the Spaniards have to retreat behind the Ebro too.
1782: French assembly proclaims to liberate all the people in Europe from their royal yoke.
1784: Peace of Basel. Bohemia, Hesse, Franconia and Thuringia-Meissen (OTL Thuringia and Saxony) become officially French satellite republics. The remaining Netherlands become part of France itself. Württemberg proper becomes a part of the Swiss republic, which is another French satellite. Sweden-Norway also has to cede Mecklenburg to the duke of Pomerania, which causes king Johan II of Sweden to doubt the cause of the Royalists. The HRE is dissolved. South Aragon (Valencia) is also ceded to France, Portugal becomes an independent republic.
1791: After the death of king Francisco I of Spain, his hot-headed grandson Francisco II becomes king instead. He pressures for war against France, which breaks out again. This is despite the fact that this coalition is even weaker than ever before. Nassau, one of the strongest German states, stays neutral, Sweden-Norway sides with France.
1791, July: Battle of Ingolstadt. French-German armies cross the Danube.
1793: Peace of Frankfurt. Bavaria, Brandenburg-Silesia, Pomerania and Braunschweig (incl. Schleswig-Holstein) are turned into republics too. Denmark proper goes to Sweden. Spain is occupied by France (except Galicia, which goes to Portugal) and divided into the republics of Castille, Asturia and Andalusia. The Spanish royal family goes to Morocco, the pope flees to Canterbury, Britain, which swears to continue the fight. This leads to a costly "perpetual war" when Britain continually tries to attack French coasts and support uprisings in Spain and Germany. Hungary has to cede the lands of the Czechs and Slovaks, which become the Moravian Republic.
The only monarchist states remaining in Western Europe are Britain, Italy, Sweden-Norway-Denmark, Hungary, Poland, and the German states of Austria and Nassau - less than ten, for the first time.