Chicago brought in tough controls. But the Republican states around it didn't. So people get guns from the nearby uncontrolled states and they end up in Chicago.
See? That's how logic works. Cause and effect.
You've actually stumbled upon a good argument without realizing it.
Let's take your logic to the next level.
Let's say the US passes strict gun control nationwide.
We have a border to the south that you Limeys don't have where we couldn't stop 12 million+ Mexicans from coming into our country. That's not to mention the millions of tons of illegal drugs that come across our southern border too. While were at it, we have millions of tons of drugs coming into the US from China. Yeah, we can't stop that either.
So how do you propose to stop guns from entering the US illegally, I'm gladly waiting for your answer.