Complex sentence: Military spending expanded, usually leading to an "imperial overreach", and imperialism created clients of ruling elites abroad that were brutal and corrupt, consolidating power through imperial rents and impeding social change and economic development that ran against their ambitions.
Split into simpler sentences: Military spending expanded, usually leading to an "imperial overreach", and imperialism created clients of ruling elites abroad that were brutal and corrupt. Consequently, the corrupt elites were then able to consolidate power through imperial rents and impede social change and economic development that ran against their ambitions.