More can always be said, but check these answers from /u/ParkSungJun, /u/RajaRajaC, and /u/I_am_oneiros
https://www.reddit.com/r/AskHistorians/comments/6z87au/why_was_the_east_india_company_so_successful_in/
https://www.reddit.com/r/AskHistorians/comments/9r30q3/why_did_the_sikhs_generally_side_with_the_british/