"アメリカの敵対者は警戒すべきです友人は慎重であるべきです"

Simplified Meaning:

The saying means that people who oppose or compete with America need to be careful because America is strong and can defend itself very well. On the other hand, even the countries that are friendly with America should be careful when dealing with it. For example, in history, countries that acted against America often faced powerful responses. Countries that are allies should also be thoughtful because being a friend doesn't mean they should take anything for granted — they should know that policies and interests can change. It's similar to having a strong and influential friend; while you trust them, you still have to be mindful of their power and the way they might act under different circumstances. This advice suggests it's smart for both opponents and allies to handle their relationship with America thoughtfully and with awareness.