Complex sentence: The protests were forcibly suppressed after the government declared martial law in the Tiananmen Square massacre where troops with assault rifles and tanks killed at least several hundred demonstrators trying to block the military's advance towards Tiananmen Square.
Split into simpler sentences: The protests were forcibly suppressed after the government declared martial law. In what became known in the West as the Tiananmen Square Massacre, troops with assault rifles and tanks killed at least several hundred demonstrators trying to block the military's advance towards Tiananmen Square.