Do you guys really think China will unilaterally invade the North American continent with an expeditionary force? Wouldn't they need to have a really BIG Navy? At present they don't even have an aircraft carrier! The PLAN is building up but they're ambition extends no further than a green water naval force capable of projecting Chinese power as far as Guam by the mid 21st century. PLAN currently is capable of no more than active offshore defense. The challenge they present to the US is largely economic. In that arena they are a formidable competitor. The 'invasion' is happening today: Chinese businesmen arriving in 747 armed with Yuans. Not PLA soldiers in battle fatigues.
