English IPA's were first brewed in England and exported for the British troops in India during the late 1700s.
IPA's were basically tweaked Pale Ales that were, in comparison, much maltier, boasted a higher alcohol content and were well-hopped, as hops are a natural preservative. Historians believe that an IPA was then watered down for the troops, while officers and the elite would savor the beer at full strength.
The leaner the brew the less amount of malt there is and less need for a strong hop presence which would easily put the brew out of balance. Some brewers have tried to recreate the original IPA with strengths close to 8-9% ABV