Complex sentence: The defences of these colonies and their cities, including Pensacola, had been seriously neglected under the Spanish rule resulting in British forces having to spend a huge amount of time and money attempting to bring them up to standard.
Split into simpler sentences: The defences of these colonies and their cities, including Pensacola, had been seriously neglected under Spanish rule. As a result, the British spend a large amount of time and money attempting to bring them up to standard.