The 20th century has told us many lessons. History does not repeat itself, but it appears that new variants of old themes keep coming back. Slowly passing the century like a movie in decades instead of episodes, we witness socio-emotional tides. The first decade, the 00s intensify the beginning of urban planning and social revolutions. The 10s show the arousal and subsequent extinction of masses of people in trenches. The 20s were described as the Carefree Twenties. In the 30s we observed the rising tides of fascist organisations followed shortly afterwards by the disastrous 40s. After the Shoah and the World War the 50s were fabulous viewed from the U.S. and Western Europe. The 60s propagated sex, drugs and rock n’ roll spreading across continents. The wild 70s became almost inescapable through the continued rise of mass media. The 80s were depicted as the colourful 80s as the 2 previous decades had set the scene for psychedelic colours. The 1990s have been coined as the gay 90s by some. Coming out as a gay person became easier and Western societies more sensitive and open to diversity. The back cover of the recent publication by Aurélien Bellanger “Le vingtième siècle” (The 20th century) speaks of the book as “roman polyphonique virtuose”. I look back on the 20th century as “polyphone” in many respects. It would be an illusion to believe we can only keep the nice sounding harmonies without the tensions or dissonances. 
10s
The 1910s have been eclipsed completely by “the Great War” between 1914 to 1918. The 1st world war certainly was the most horrific period of the decade of revolutions and mass arousal. From a global history perspective the years preceding and shortly after the humanitarian disasters deserve more attention, if we were to derive lessons for prevention of other world encompassing wars of imperialist states. The numbers 1st, 2nd, … 3rd (?) world war suggest an unescapable numbering of events. We no longer can think in this trivialising logic of war or historical determinism. Empires go to war more easily than democracies. This was the social scientists’ consensus after the Great War. It took several years for many European states to turn more democratic, allowing women to vote, or introduce more robust health and social security systems. Powerful aristocracies would not cede power easily, only the widespread poverty after the Great War and the human losses discredited many aristocratic regimes throughout Europe. The imperialist dominance of the beginning of the 1910s produced a spirit of ruthless conquest and exploitation of colonies around the world. It took another global war and almost half a century to dismantle these regimes. To understand global alliances and impediments of wars in the 21st century, the early 1910s are instructive as they inform the restitution of artefacts debate in the 2020s. In the history of ideas, the 1910s are probably best characterised as the period of attempting to turn “grand ideas” into political facts on the globe. The rise of Marxist ideology, liberal and fascist counter movements started to take powerful roots at the end of the 1910s. All these ideas and factual changes of the maps of power still seem to govern a lot of international politics even today. 