In 1845 the U.S. annexed the Republic of Texas, which had won de facto independence from Mexico in the Texas Revolution (1835–36). ... Polk found a rationale to justify an attempt to take that land by force when U.S. and Mexican troops skirmished north of the Rio Grande on April 25, 1846.
Well when deciding on weather the country's would like to attack or not is really up to them it could be for reasons like territory or it could be because they want to get back at them for something they lost; it all depends on what their goal is in attacking another country. As for if it's okay well at any time they can attack not necessarily there has to be a certain day or time to att
