Complex sentence: Both the Borgstrom and Butehorn tragedies occurred before the Sole Survivor Policy was put into effect in 1948, but they, along with the deaths of all of the Sullivan brothers in 1942, helped lead to it.
Split into simpler sentences: Both the Borgstrom and Butehorn tragedies occurred before the Sole Survivor Policy was put into effect in 1948. They, along with the deaths of all of the Sullivan brothers in 1942, helped lead to it.