Complex sentence: The M88A1 was designed around the now obsolete M60 Patton tanks, so it was in light of the fact that two M88A1's were required to life the new M1 Abrams tank that the decision was made to upgrade to the M88A2 in 1991.
Split into simpler sentences: The M88A1 was designed around the now obsolete M60 Patton tanks. It was in light of the fact that two M88A1's were required to life the new M1 Abrams tank that the decision was made to upgrade to the M88A2 in 1991.