Complex sentence: Up through the 1950s, they were commonly given to any visiting head of state, but the 1960s, following the assassination of John F. Kennedy, they became increasingly rare are generally reserved now for space exploration triumphs, military honors and sports championships.
Split into simpler sentences: Up through the 1950s, they were commonly given to any visiting head of state, but the 1960s, following the assassination of John F. Kennedy, they became increasingly rare. They are generally reserved now for space exploration triumphs, military honors and sports championships.