Comment by MisterMower

How does one nation following an ethical code encourage others to follow it as well?

Following an ethical code in international affairs constrains the nation following it. It provides an asymmetric advantage to others who choose not to follow that code.

This is partly why China has become so powerful over the past three decades. They chose to ignore western ethical codes around intellectual property rights, fair trade, environmental protections, and human rights. They are powerful today in no small part to their willingness to disregard these things.

This is difficult for people to understand because in interpersonal relationships following an ethical code is 100% the path to healthy and meaningful relationships, and most modern history education attempts to anthropomorphize past interactions between nations. But the cold fact is that international politics is nothing like interpersonal relationships.

A nation can encourage other nations to follow their ethical code by threatening to use force if they don't. They can create incentives to encourage nations to change their behavior through trade or treaty. But I can't think of a single time in history when a nation was such a shining star of morality that they inspired other nations to change their ways and adopt their ethics.

You can't expect other nations to respect your nation's moral and ethical values when they don't care about them in the first place and in fact hope that you choose to follow them to the fullest extent so that you're easier to compete against.