USN and USAF can do in the domain of each what US Army (AUS) and USMC did in Desert Storm and then in Iraq in 2003. In fact if the US engaged in a major war against a major power its multi-domain warfare of integrated combat by Army, Navy, Air Force would be awesome.
Iraq is the largest country geographically the US has ever invaded. In Iraq the US operated with troops inexperienced in large scale maneuver warfare. Iraq is bigger than France and it is bigger than Germany; bigger than Mexico (S Vietnam was not an invasion although many would argue the point). In the early 19th century US had some border engagements against Canada but US did not invade our friendly neighbor to the north, as some tag it to be. US hasn't invaded Russia or China nor would the US do so alone, if at all and if ever -- each country deserves special attention of course (the post WW I activity in the Russian civil war was not an invasion).
Iran is more than three times the size of Iraq. While Iran does not have a Tigris and Euphrates Iran does have numerous smaller rivers which would not be an obstacle and Iran has more major urban centers, to mention but two significant elements of entering Iran. US access to Iran exists from Iraq, Saudi Arabia, Afghanistan and at the Strait of Hormuz area (Turkey would be dubious politically) which are excellent staging areas also. NK is heavily defended in each respect -- land, air, sea -- and moreover NK and China are the only two countries among those mentioned that has engaged US forces in a war of significance, which is the Korea Conflict in the early 1950s.
There are a multiplicity of factors to consider beyond these of course but this is a summary introduction. Your post #23 btw is consistent with the assessments of the US Naval War College concerning the PLA Navy. The post didn't mention Japan but let's. The PLAN well exceeds the Japan Maritime Self Defense Force (Navy) in total tonnage and in number of ships, which aren't the only measures but the two are a good starting point. Naval War College in Newport RI considers the two naval forces as equal at the least -- that's China and Japan. In fact the College evaluates full out naval warfare between the two only by saying it in this way, i.e., if the Japanese Navy had a good day it would defeat PLAN. In other words PLAN has much to worry about against the JMSDF. Why? For one thing China has virtually zero naval history in war -- or at all. PLAN has no culture of fighting; it hasn't any depth of command or of ships crews in fighting in a war. That isn't all of it by any means, but it gives some idea.
In contrast, Japan has a history of naval warfare that is great and extensive. It's officers are well versed in naval warfare and the past experience of it to include a zillion case studies and lessons. Training regularly at sea under extreme conditions is the rule for JMSDF whereas for the PLAN it's a new and limited experience. Japanese naval personnel are better educated going in and once they're in they are better educated and trained than PLA naval personnel. In Japan the sea is an adventure to be experienced whereas Chinese culture going back thousands of years is to fear the oceans out there; Chinese cherish the land while viewing the oceans and seas as forbidden terra incognita. Japanese technology is superior as are its operators; JMSDF commanders have a deep knowledge and analysis of both their own naval warfare and history and in general. There's this and much more and it should be giving the CCP Boyz in Beijing hives over the capabilities of their armed forces against a major power(s).
