US vs Iran
The current US administration’s objective is to effect a regime change in Iran. This, theoretically, could be achieved in three ways: a “colour” revolution  as seen in some Eastern European countries, a CIA sponsored coup d'etat (like Iran in 1953  Chile in 1973 ), or a forced regime change.
Ever since the Iranian revolution, US has been trying to use any means short of an invasion to effect a regime change, without any success. United States froze Iranian assets, applied comprehensive unilateral sanctions, threatened to punish other countries who wanted to invest in Iran (investment in oil industries) and even encouraged and supported Saddam Hussein in its war against Iran, without achieving the desired results. What is left is to either accept a grand bargain with Iran or use military means to change the regime in Tehran by force. And since this administration has consistently refused any kind of rapprochement with Iran, this leaves us only with the military option.
The Military Option
Anyone with a brain size bigger than an egg can see that, irrespective of the technological prowess and the size of the army, invasion of a big and mountainous country like Iran will neither be easy nor quick.
Iran, with a population of over 70 million people and an area of nearly 1.64 million square km., is not a small country. Topographically, the country is similar to Afghanistan, covered with high mountains, some of which are as high as 5000 meters. Iran borders Afghanistan (936 km), Armenia 35 km, Azerbaijan-proper (432 km), Azerbaijan-Naxcivan exclave (179 km), Iraq (1,458 km), Pakistan (909 km), Turkey (499 km) and Turkmenistan (992 km). Iran also has 2240 km of coastline of which 1700 km is along the Persian Gulf and adjacent Gulf of Oman in the south .
Dr. Abbas Bakhtiar