Disclaimer: this is related to "homework" so please refrain from answering the underlying question, answering that one is my job, I just need a bit of help.

When the EIC starts its private military they end up deploying some of their sepoy regiments (native infantry) to foreign conflicts, mostly British imperial wars. I hope to compare this pattern of Indian troops deployed to foreign territories to the prevalence of such "deployments" prior to company rule.

So as far as I can tell Indian troops may fight abroad for three reasons, 1. an Indian state is invading a foreign territory; an Indian state mobilises its forces to aid a foreign ally; OR 3.an Indian mercenary company gets hired to fight in a conflict outside of India.

From what I can tell the first case rarely comes up, there is the occasional foray into Afghanistan but that's about it.

The second and third especially is what I suspect I need to establish.

The problem is that given how interconnected India has always been to surrounding regions through trade, an Indian mercenary company might well have participated in basically any conflict in most of the eastern hemisphere which makes it a bit hard to delimit where to look for sources that mention of Indian troops outside of India.

So here is the question: How should I go about searching for sources attesting the participation of Indian troops in foreign conflicts without having to meticulously hunt down literally every primary source, no matter how fragmentary, related to any military engagement in the area in question (basically the Middle East, Indonesia, South-East Asia, East Africa, and presumably China- as well as possibly even parts of Central Asia)? I am sort of hoping to get refered to a book that conveniently concerns Indians fighting outside of India, I'd still have to do a lot of work but it at least would be much simpler.