An attack on Earth that killed millions.
The Xindi were a group of species from the Delphic Expanse, and they had been told by a mysterious faction from the future that humanity would one day destroy their homeworld. Convinced by this warning, the Xindi Council decided to strike first and began building a weapon capable of destroying Earth.
In 2153 a Xindi probe crossed from the Expanse and carved a trench across part of the planet, from Florida to Venezuela, killing millions. The attack caused a wave of shock and grief throughout Earth, and Captain Archer, whose own world had been shaken, was ordered to take the Enterprise into the Expanse to find the Xindi and stop them before they could launch their weapon.
The mission was long and dangerous. Enterprise faced hostile species, spatial anomalies and treacherous alliances, and many of the crew were changed by it. Trip Tucker, who lost his sister Elizabeth in the attack, was one of the most affected. Eventually Archer and the crew proved that the Xindi had been manipulated, helped bring some of them over to humanity's side, and stopped the weapon.