It wasn't under attack, the right was the movement of internationalism, and the left was the party of tariffs and protectionism for over 70 years. These things seem to switch every 70 years or so because internationalism / nationalism isn't a fundamental belief of either the left or right. What really divides the parties is individualism vs collectivism. I feel like nationalism is far better suited to individualism than internationalism, but this isn't obvious to everyone.