Why did Panama declare its independence in 1903?

A simple answer to a complicated issue.

I wonder if it's still a tax haven for billionaires and multinational corporations? or was that only before 1999?

Panama is definitely a pro-US country since the US helped the Panamanians to achieve independence and sovereignty

One of it's more famous citizens was the prima ballerina Dame Margot Fonteyn who was married to a Panamanian politician and retired to, died and is buried there.

and they did, didn't they?

Still a tax haven?