Russia has begun delivery of S-400 air defence system to India. Its worth knowing ;
1. What is it ?
2. How important is it for India's security ?
3.Why US is concerned about it ?
Many such questions are answered in an article ;. https://indianexpress.com/article/explained/s-400-purchase-air-defence-system-india-us-relation-7626388/?utm_source=newzmate&utm_medium=email&utm_campaign=explained&utm_content=6386461&pnespid=G7sj.0hT5CwUzQWR8MnAS1hWoE44mbFx_1VSBLkDK4HK61seM3WdFIYKcFk1N0GM4v00j6Ka