Equation
Lieutenant General
It's an old truth that ships are the cheapest way to move objects around (that's why we still have so many ships today). Whoever doesn't have harbours for ships to do the job must pay about 20-25 times more per transport mileage. It isn't impossible to get one or another kind of resource into China, but without SLoC access China, like every other nation on earth, would be have to pay much more for a rather limited quantity.
Yeah but those Navy ships has to board and search every single cargo vessels to make sure no materials are heading to or heading out from China. That takes a lot of man power and equipment to search and look at each and everyone of them, at the same time fighting off attacks from land base missiles and mines laid out by fishing vessels that the navy didn't cover. Naval patrols by air therefore requires more fuel, at the same time putting more man hours flight and pressure on those planes air frames,therefore, more planes needs to be order to replace the old ones, while at the same time fighting off various SAMs and radars from China. Does the US Navy has enough ships to patrol 100% of the entire world's sea coast for 100% at all times in order to effectively "blockade" China? And another matter to look at are the economic impact on both sides, since Americans are less tolerable today about unemployment and the current economic outlook, imagine if it's an election year. Think the OWS was pretty vocal wait until the next one if this ever occur (which I hope not). War today is not simply by force alone, it's EVERYTHING on the table, from politics the to economy comes into play. Oh, need I mention about the cyber warfare that's going to happen and yes, China has a lot of nationalistic proud people to do it.