They entered into a country and killed the civilians then what do you expect a country to react?
Investigations needed to reveal the full story of who is behind this. But It is proven multiple times that Pakistan sponsored terrorism to attack India for example 2008 blast carried out by LeT organization operating in Pakistan and US confirmed it too and then in 2016 and then in 2019 and a few hundred times so we need to turn back the history to know the full story.

And I am asking again if the same thing happened in the USA how they will react? Anyone can answer my question.

Please feel free to.
Did India do any investigations before they started attacking Pakistan, calling it a revenge by saying that they've targeted terrorist camps? They didn't, and is there any proof that the killing of the innocent tourists in Pahalgam wasn't a planned political move by Modi to first start a war by doing that, taking revenge for it, and gaining sympathy from its people so that he can get more votes in the upcoming elections? How would you disprove that? You can't, because you only use words, and words can't be taken as proof or evidence for something this serious.
Terrorists don't have regions or religions; they don't do what they do for specific countries. They might hide anywhere in the world, but you can't blame a country where some terrorists might manage to hide by keeping their identity hidden. Even in India, the Hindu population often kills Muslims only because of their religion; shouldn't they be called terrorists then? Why doesn't the Indian government start bombing their houses or camps, as they call it?
It's all hypocrisy and nothing else. You can't see the reality if you close your eyes.