The question was not if the U.S. could Nationalize companies that are based in America, it was when has America done so? We pay the investor for the use of his money, we don't steel it as Mossadegh did, so you condone stealing if it is done in the name of the people of Iran? but is it not still stealing, the moneys invested were not returned, and the use of those moneys wasn't paid for, a thief is still a thief, and Mossadegh was a thief no matter how you dress it up.
Surprisingly investing in a company does make you a owner in the Company, if the returns are not good enough, if you own voting shares you can change the leadership of the company, if you don't own voting shares, you still are a owner in the company, and as such you remover the moneys that make you a owner and invest them some were else and divest your self of said company, and if enough other investors agree with you guess what happens to the company, and that is exactly what happened to Mossadegh, he was voted out by the stock holders, they had influence in their countries, and they influenced Iran, and change the leadership of the company.
You forget fact that the moneys weren't paid back, (Theft on a Grand Scale) and if you change the laws to make theft of property legal, remember the oil was paid for and royalties were being paid, the Iranian Government was getting its cut of the money, from the sale of the oil, why shouldn't the offended parties change the laws again if they can, when you start to cheat the system and become a thief as Mossadegh did then expect the people who you stole from to play rough, and if you can't play in the same league expect to lose, and Mossadegh lost and paid for his crime.