Battle of plassey and battle of buxar are the landmarks in the indian history. Had the east india company lost either of these, india could well had been colonalized by french!

it was middle of 18th century and both britishers and french were doing trade in India equally. French also had a trade company with identical name.

like the east india company of britishers , the east india company of frech were involved in aggressive trade in eastern coasts,  main centre being the bengal province where they had allied with the bengal - nawab Siraj-ud-daula.

siraj-ud -daula was a powerful ruler with 50 K amry head count and had all the latest artillaries supplied from france.  

Bristish east india company recognised the importance of bengal as a trade  gateway to indo china. so they started showing interst in bengal.

Siraju daulla didn't appreciated the east india company's intervention. later on political issues emerged that lead to a full fleged war at plassey, called battle of plassey between french backed up siraj ud daulla and east india company. Mir jafer was one ambitious commander of siraj-ud-daulla's army. he supported the east india company and because of his sudden alligment with east india company , the bengal army faced huge loss and eventually the east india company emerded as victorious.

Mir jafar was rewarded for his support to british east india company and he was made the next nawab of bengal.

This was the landmark because , after this the east india company started to envisage interest in the political scene apart from just trade.

And after the victory of east india company in battle of buxar seven years later against the mughal ruler shah alam, they started to push its political ambitions in the indian sub continent.