India bought S-400 air defence units from Russia in 2018 despite US' threat of sanctions

India had signed a $5.43-billion deal with Russia to procure five S-400 air defence units in 2018. S-400s are the equipment which reportedly shot down Pakistani drones launched against multiple Indian cities. US had threatened India with sanctions under Countering America's Adversaries Through Sanctions Act (CAATSA) in an attempt to deter countries from buying Russian military equipment.