Look at that border!
The sentence should be: You crossed the Cambodian border. In that instance, Cambodian would be the adjective, as it is describing the noun which is border.
The sentence is: "I was thrice apprehended while in the act of crossing the border with Mexico."
These border ruffians seem to never get the message.
There is not an international border between Europe and Asia
I became an immigrant when i crossed the Canada border over to the U.S. border.
YES YOU Can.!
intensifiers
Immigration was largely controlled by border ruffians with little oversight
"Is" is the verb in that sentence. It's a linking verb that connects the subject to the subject complement. As a compound adjective, "cross-border" should be hyphenated.
President Trump has promised to build a wall on the US-Mexico border.
Set your fence boundary at least five feet inside of your neighbor's border.