When examining previous historical eras, how come the different eras of the 20th Century are distinctively categorised by the decade, while previous historical eras are often categorised by the century?

by sammyjamez

So whenever I delve into previous historical eras between the 20th Century, I barely see any difference in the cultural mainstream or the significances between the decades (such as cultural, political or technological differences between the 1850s and 1860s for example) while in the 20th Century, the differences between the decades are often quite apparent such as

the 1900s and 1910s was the beginning of the modern era and the adaptation to more modern technology and the implementation of said technology in the First World War and the political shift that happened during the war and after;

the 1920s as the political shift after the Great War, from the beginning of the declining influence among the Imperial Powers

the 1930s as the Great Depression and the rise of Fascism

the 1940s, the Second World War

the 1950s, the Baby Boomers era, American exceptionalism, the rise of the American Economy and the beginning of the paranoia against Communism during the Cold War

and so on.

How come this is the case? Does the familiarity (or the youngness) of the timing have any significance on the clarity between the decades in the 20th Century or perhaps there is more clarity in the archaeological remains of the decades? Perhaps the technology that was used during that century allowed for better preservation of historical and archaeological evidence when compared to other centuries which might have been lost through time or were influenced by other factors during that time (such as how the other nations were identified during the Age of Discovery or the Age of Imperialism)?

mimicofmodes

Does the familiarity (or the youngness) of the timing have any significance on the clarity between the decades in the 20th Century ... ?

Yes.

Archaeology and technological preservation don't come into it: archaeologists are very rarely doing work on 20th century sites. It's solely a matter of perspective (much of the century is within living memory of roughly half the population) and pop culture.

I have an older answer, We distinguish the differences between the decades of the 1900s (70s, 80s, 90s) very distinctly. What were some specific differences between the decades of the 1800s?, which deals with the issue of significance between decades/sub-periods within the 19th century.