Several of the various areas that are being applied to modern history are better connected to the 20th century than to other areas. North American peoples have become particularly prominent in this period, and New York City became one of the world's leading cities. Secularism became especially important, International government structures developed; sports and games proliferated, applied science greatly expanded, and new forms of buildings and arhitecture developed.
Subdivisions of this century are being established. The Early-mid 20th century (1921-1940) is a new stub, the Mid-20th century (1941-1960) which includes World War II and the early Cold War period is not much better advanced, and the late-mid 20th century (1961-1980, Vietnam & Middle Cold War) is not quite ready for much discussion. So far, I don't have many events to put in the late 20th Century (1981-present), but this should be developing before long.
The future is rather difficult to follow, until I have better methods from other areas of study. I have opened investigation of the 21st Century by looking at the immediate future (2006 - 2010), but don't yet have details.