USA Lieutenant Napoleon Diana was waiting on the Rio Grande sent from Louisiana by the government.
The reason why he was waiting there was for a war with Mexico.
The reason why there are many soldiers are waiting to take revenge on the Mexicans for making the Texans suffer as they put it.
So while there were recruiting many Texans went there for that reason.
In 1845 President James K Polk was sending John Slidell to Mexico to settle disputes.
When conflict with brewing near John, Polk sent General Zachary Taylor and soldiers to help him out.
Taylor refused a proposal and the Mexicans attacked him across Rio Grande.
War was declared it was called the Mexican war of 1846.
Winfield Scott was the new commander of the army after Taylor became a national hero.
Scott took control of the city after sailing towards Veracruz and Santa Anna have failed to stop the US from advancing.