Complex sentence: Since the early 1970s, influenced by the U.S. gay liberation movement and the 1968 Tlatelolco massacre, a substantial number of LGBT organizations has emerged; visible and well-attended LGBT marches and pride parades have occurred in Mexico City since 1979 and in Guadalajara since 1996.
Split into simpler sentences: Since the early 1970s, influenced by the United States gay liberation movement and the 1968 Tlatelolco massacre, a substantial number of LGBT organizations has emerged. Visible and well-attended LGBT marches and pride parades have occurred in Mexico City since 1979 and in Guadalajara since 1996.