USA cannot "jump in". USA does not have any bases that could take part directly in a border war between China and India. China and India share a land border. None of the other US allies share a land border with China.
USA can cause problems in Asian littorals with its navy. But as long as China finishes off India within a few weeks, China can easily defend against any US military action too. Go in, mess them up badly, and pass the wounded animal to Pakistan to deal with.
I love to read your posts as they are very entertaining. you come up with nice comedy. Thank you very much for entertaining me here on defence.pk. Anyways, on a serious note are you aware of US military capabilities? i doubt so. you are ignoring the fact that US has aircraft carriers. Do you know that the US had dispatched an aircraft carrier to India during the 1962 Sino-Indian war? well it can do the same again. find out about the capabilities of US carriers incase you don't know.
Now for the question of US overseas bases, The US military bases in south-east/ east Asia are in the philippines, japan, south korea, singapore which can be used to strike the northern and eastern parts of china among others. It has a strong base in Diego Garcia.
List of United States military bases - Wikipedia, the free encyclopedia
United States military deployments - Wikipedia, the free encyclopedia
It also has bases in the middle-east which are being used for WOT in afghanistan and pakistan. It has military bases in afghanistan.
This i why i said that in case of a Sino-Indian war, the "US WILL JUMP IN" and will use these bases. And what makes you think that India will not offer its military facilities and bases to the US?
It is not necessary for the US to have allies who share a land border with china as 21st century war includes aerial and naval warfare apart from land warfare. And since India shares a border with china, US troops can be transported to these areas either through land or through air once they reach India.
You think the US will cause problems in Asian littorals with its navy, i think it will cause a havoc.
And i don't think the US will wait for few weeks for china to finish off India and then step in. It is keeping a watch on china at this moment as well and will dispatch its military immediately should the need arise in accordance with their strategic policy.
As for your statement that china will finish off India within weeks, it seems to me that you are still living in 1962, and are unaware of India's current military capabilities and near future acquisitions.
India can do significant damage to china in retaliation as it has the weapons required to do so.
contrary to your statement that china can easily defend against US military action, i would say "not so easily because of US technological edge". Eg. US F-22 RAPTORS are already in service while chinese 5th generation fighter prototype is in testing phase and will take a few years to be inducted.
India has contigency plans incase of a two-front war if it happens. so forget that the last part of your post will ever manifest into reality. Also US will not allow china to weaken India militarily or economically as it against their strategic interests.
In light of the above mentioned facts, i conclude that THE US CAN AND WILL JUMP IN IF IT IS NECESSARY.