It took several iterations of territorial expansion for Germany to be considered an actual fightable foe. Austria, Memel, Sudetenland, the rest of the Czech lands, Poland. Even after the invasion of Poland, when war was declared, it was a Phony War in the beginning. The fighting in the West only really started in 1940.
There is a very simple way of telling a country to revert course: deem their passports no longer valid. Fundamentally, the right to move between countries is provided by the International Covenant on Civil and Political Rights Article 12 which says "Everyone shall be free to leave any country, including his own" but then continues "The above-mentioned rights shall not be subject to any restrictions except those which are provided by law, are necessary to protect national security, public order (ordre public), public health or morals or the rights and freedoms of others, and are consistent with the other rights recognized in the present Covenant".
For China, it'd be even easier since they signed but didn't ratify this treaty despite it has been signed in 1966 and in force since 1976.
We're going to see a repeat of these events 20 years from now when Vietnam's economy grows, thanks to manufacturing relocation, and we're just as dependent on them for various things. Right now the world is hoping and praying that Vietnam will liberalize when money flows in, but it's more likely they'll follow a similar path as China, albeit less powerful.