אחיכם יעלו למלחמה ואתם תשבו פה Moses asked the two tribes that wanted to sit out the war "Your brothers go up to war and you will sit here?" The idea was that the area beyond the Jordan river was empty. Sihon and Og had attacked the children of Israel and lost the war, so that whole area was empty and 2.5 tribes wanted to stay and settle there while the rest of Israel would enter the land of Canaan to fight and settle. Moses did not like the idea of these 2.5 tribes staying behind. [Two tribes asked originally but in the end 2.5 settled there] [Two tribes asked originally, but in the end 2.5 settled there]. The end result was they in fact joined in the war, but afterwards went back to settle that land beyond the Jordan River. However I have never been able to figure this out very well since in fact the whole land was not conquered until King David conquered Jerusalem many many years later; and the five cities of the Plishtim also were not settled as far as I can tell.
[Besides that, I think it is best to take care of the Iranian problem before it gets out of hand. Like Alexander the Great said when he was asked how he reached his success. He said because when there was anything to take care of he took care of it right away without delay. That applies here. Better take care of the problem before it is too late. I would not worry if anyone wants to help. If the USA wants to help then fine, but if not Iran is a threat to all Western Civilization and need to be put in its place.