As the story goes, in 1990, the US did intervene in the sub-continent, and exchanged spy satellite photographs withf the Pakistanis and the Indians. It also shared this intelligence with the Chinese and with the USSR.
What the photographs showed was what each side had armed ready for the other. In other words, the Indians saw the Pakistani planes loaded and ready with nuclear payloads, and vice versa.
Sometimes, detente is the best way of achieving peace, whilst not removing the immediate threat. This was much the way of the Arms Control Treaties of the 1970s and beyond.
In due course, the US, China and Russia will probably collaborate together to bring about a lasting resolution to the sub-continent which, of necessity, will require: 1) resolution of the Kashmir situation (before either the UN Security Council - possibly through the Trusteeship Council); 2) compensation (ie: economic and political aid) to both countries on account of Kashmir; 3) a de-militarisation force installed into place in Kashmir; and 4) bi-lateral disarmament of the existing nuclear arsenal of both countries (again, in return for appropriate economic and political aid).
