Good questions - the world systems folks really do not give any convincing causal explanations of the trends they claim. Superior ways of mobilizing resources and projecting military power are just buzzwords if taken out of specific geo-political contexts. It could be argued, for example, that Pax Britannica was an exception rather than the rule due to specific geo-political circumstances. Assuming Gershenkron's argument about exceptionalism of British industrialization (which btw runs contrary to Marx's claims) and that the belated industrialization (France, Germany, Japan, Russia) was organizationally superior to earlier industrialization (England) - Pax Britannica can only be explained as a historical accident resulting from geo-politcal situation of that time - i.e. reliance on overseas colonies to mobilize material resources, and the naval strength of England to thwart that mobilization in organizationally superior France and Germany.
The counterfactual to this argument is that the absence of the British Navy effect produced a cartel system far superior to British industrial capitalism. There are three such cases: the US (cf. Chandler's _Visible Hand_), Japan (Meji restoration) and Russia - each one of them using industrial organization similar at its core (cartels organized around financial institutions and national in scope). Germany can be put in this category as well if we consider its chemical mfg that was able to substitue some of the raw materials imported from colonies (thus bypassing the effect of the British Navy).
>From that standpoint, Pax Britannica appears to be a historical accident
unlikely to be repeated - and with that the whole world system argument
falls like a house of cards.
Another point is that if superior organization of resource mobilization (cf. cartel) is at the core of shifting world power - that is a powerful argument for undisputed dominance of the US as of now - for ther eis no more efficient system anywhere else -- unlike the situiation in the 19th century, when the "continental" cartel system was clearly superior to "family capitalism" developed in England (which proped up only by England's geopolitically strategic position).
wojtek