Complex sentence: Fort Richmond would be rebuilt in 1740, attacked by another tribe in 1750, then dismantled in 1755 when forts Shirley (also called Frankfort), Western and Halifax were built upriver.
Split into simpler sentences: Fort Richmond would be rebuilt in 1740, attacked by another tribe in 1750. The fort was dismantled in 1755 when forts Shirley (also called Frankfort), Western and Halifax were built upriver.