British historic architecture seems very simple compared with fellow European nations like France.
Why is this? Considering Britain's empire wealth that is generated from, surely the British could've put that wealth to impressive buildings/palaces?
How do you mean? What buildings are you specifically thinking of?
In my opinion, Westminster palace and Canterbury cathedral and the Crystal Palace are all very impressive. I don't think it is necessarily true that British architecture is "simpler" than other European architecture.