While revising, I have realized that ninety percent of all the history I have ever done has been the history of six countries between around 1900 and the present. Here they are, complete with a crude trend line for their overall influence/affluence:
- United States (Up)
- Britain (Down)
- Russia (Down, Up, Down)
- China (Down, Up)
- Japan (Up, Down, Up)
- Germany (Up, Down, Up, Down, Up)
Top performer: USA
Most improved: Japan
Most troublesome: Germany
Most dramatic: Russia / China, tie
Most graceful decline: Britain
The history of other countries has mostly been bound up in their importance, vis a vis this crew. For instance, the transition from British to American hegemony in the Middle East, the role of France in developing and maintaining the interwar order in Europe, India as the jewel of the British Empire, American containment strategies in Europe and Latin America, or the various imperial phases of all and sundry.
I am fairly sure you could get a distinction on my International System 1900-50 qualifying test without mentioning any other states.