Complex sentence: However, as the Empire grew, the cost of maintaining communications, garrisons, civil government, etc grew to the point where new challenges, such as invasions and crop failures, became unsolvable by the acquisition of more territory.
Split into simpler sentences: However, as the Empire grew, the cost of maintaining communications, garrisons, civil government, etc. grew with it. Eventually, this cost grew so great that any new challenges such as invasions and crop failures could not be solved by the acquisition of more territory.