Houston was the most populous city in Texas and the fourth most populous city in the United States.
In the second phase of the alien attack on Earth, a City Destroyer was on its way to Houston. In the chaotic evacuation, almost two thousand people were killed and when the Destoryer arrives, just ten percent of the population is still in the city. President Thomas Whitmore decided to authorize a nuclear strike against the City Destroyers. A B2 Spirit was the close to Houston, in which Whitmore decided to attack this Destroyer first while knowing that he will kill thousands of Americans.
Before giving the sign of attack, the President says "May our children forgive us", knowing that his desperate decision is not in line with his own morals.
After the missile explodes, an AWAC pilot confirm that Houston has been destroyed but that the City Destroyer is still intact, with no damage at all. At this point, the President decided there is no point to continue attacking and immediately called off the strike.