At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga.
Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus.
Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
need three reasons what i have so far
• The US should be independent
• Belief that the expansion of the US throughout the America was justified known as Manifest destiny
You need to pick your basis for deciding whether things are justified or not. Do you mean morally? Economically? What are your guiding principle here? Are you an "ends justify the means" kind of person, or a "the good of the many outweighs the good of the many" person? You first need to establish your moral principle and philosophy before you can judge an action within that framework.
i just need one more point to add to my thesis stament
Not the answer you are looking for? Search for more explanations.
I would say you need more than that. Your first point ("Yes") is not a reason, but a conclusion. Your second seems odd, because you haven't explained how the independence of the United States would be influenced by going to war, or not going to war, with Mexico -- and you need to do this, because there is no obvious connection. For example, I sure can't see how the two are connected. Mexico was in no position to threaten the indenpendence of the US in 1846. Finally, your third point, unless you explain it better, is just a restatement of your conclusion. You can't really say "The war is justified by manifest destiny" without explaining the connection.
From the hints you've given here, I would say you might consider making an argument along these lines:
(1) Mexico started it, by attacking the army of General Zachary Taylor, who had been orderd to defend territory on the Rio Grande claimed by the United States as a consequence of the treaty between Texas and Mexico by which Texas first became independent.
(2) The US had tried to peaceably negotiate the disputed territory that had been part of Texas, by sending John Slidell to Mexico City, empowered to offer Mexico substantial amounts of money for the disputed territory.
(3) Even if the US had seriously provoked the war, and taken advantage of the fuzziness of the relevant treaties, the people in the relevant regions (Texas and Alta California) would be better off under American than Mexican rule, which was confused and corrupt at the time, with the Presidency rapidly changing hands and democratic traditions abandoned. In some cases, e.g. settlers who were originally American, those who lived in these regions actually had asked to be part of the United States. (Certainly this is true in the case of Texas.)
(4) The only basis by which Mexico could claim any superior right to rule these lands is that it had conquered them first. The Spanish aristocracy of Mexico had no "original settler" claim to these lands, since they had acquired them only by displacing and conquering the original Indian and Mesoamerican inhabitants. This is pretty thin stuff. If you want to say the United States was a thief to take California from Mexico, for example, the Mexicans only claim against that is that they stole it first, from the Indians. Not a very impressive moral claim.
You'll want to watch out for, and perhaps think up defenses against, the counter-claims that the Americans certainly did not promise (and probably did not actually) rule the native populations and better than the Mexicans. (Treatment of American settlers is a different question.) Also, slavery was illegal in Mexico, but not in Texas, so the US conquest opened the door for the important of a vile institution. Finally, if no respect is to be given to who conquers a land first, then there is no moral argument against Mexico, should it become strong enough, reconquering the Southwest.