Let me expand, if I may, on an earlier post (#14) where I introduced the primary theories of the relationship of power to international relations and the cycles of war.
In the Power Transition model, the theory I am convinced best describes circumstances since the formation of modern nations in the late 18th century, a secondary “great power” will emerge to challenge the dominate nation. Whether war results depends upon a number of circumstances most simply described by the author of this theory:
“An even distribution of political, economic, and military capabilities between contending groups of states is likely to increase the probability of war; peace is preserved best when there is an imbalance of national capabilities between disadvantaged and advantaged nations; the aggressor will come from a small group of dissatisfied strong countries; and it is the weaker, rather than the stronger, power that is most likely to be the aggressor.” – A.F.K. Organski, World Politics (1958)
U06ams7 (post #22) described a most interesting variable to the circumstances in describing the West’s impression that the USSR had relative parity with the US. Although this in no doubt influenced some of the responses of the US (the Cuban Missle Crisis, for one), it was the US, not the USSR, that always believed the world was on the brink of war. But despite the Western belief that for decades there were two superpowers, the Soviets knew they were never as strong as the dominant nation – and acted accordingly (Khrushchev would have been an extraordinary poker player!).
And as Charles Albert pointed out (post #23), the expenditure of that challenge cost them dearly, certainly destroying their chances to challenge again for decades, if ever. And although they have been a great power since 1860, they may already be well on the way to becoming a third rate nation on the periphery of international power relationships.
The next challenger to the dominate position, under this argument, would probably be a nation growing in power in relation to the dominate nation. That, as already pointed out, would likely be China or even India. Whether this will result in violent confrontation has a lot to do with how fast the challenger approaches the power level of the dominate nation. (A.F.K. Organski & Jacek Kugler, The War Ledger, University of Chicago Press, 1980)
As in all things of history: time will tell.