Wrong buddy.
What happened when the USSR invaded Georgia in 2008? Or when North Korea sunk a South Korean battleship, and then bombarded a South Korean island? Why didn't America stand up for their allies?
The answer is nukes. America keeps huffing and puffing at North Korea but eventually they had to let North Korea get nukes, and couldn't stop them. They also warned Russia against invading Georgia (who was a close friend of the US), but Russia invaded anyway and America said nothing.
Pakistan has far more nukes than North Korea. America doesn't attack countries with nukes, we have seen this proven time and time again.
And even if we were to talk about purely "conventional" warfare, then look at what happened in Vietnam or Afghanistan. America still cannot control Afghanistan after ten years, now imagine how long it will take to bring down a regional nuclear power like Pakistan.