31. The Battle Of New York Mentions
Though The Avengers very much showed Loki as the master of his own plan to invade Earth, Infinity War changes that story somewhat as Bruce Banner confirms to Tony Stark that it was Thanos who SENT Loki to Earth for the invasion.
That battle hangs over Stark in particular as an extrapolation of his PTSD storyline that has run through the MCU since Iron Man 2, and it's a clever way to tie Stark and Thanos together in a more tangible way. They're treated like old enemies who share an experience - New York - and it really does add a whole new level to Tony, who seems consumed by a personal need to make Thanos pay.
Right at the start, the battle is also alluded to by Thanos as he holds Loki's failures over him.