I think we can encourage other nations to vote to join the USA. People around the world voted and continue to vote to join the USA with their feet.
Joining the USA will improve the lot of third world nations that would join our union. For one thing, it would mean massive public investment to build highways, roads, water generation and distribution networks, power generation and distribution networks, harbors, schools, hospitals, and other infrastructure. It would also mean extension of US labor, environmental, occupational health and safety laws to the people of that country. The economy of nations that become states and territories of the USA would boom.
Incorporation of the USA would also mean the people of these nations will be able to enjoy freedom they're not enjoying now. No more rules requiring the wearing of barakas. No more prohobitions of women from driving. No more slavery.
Not to mention nations that join our union will be required by the US Constitution to maintain republican forms of government otherwise the USG steps in and steers that state towards democracy.
And nations that become states and territories of the USA will also add to America's wealth and power as well. If America annexed and rebuilt every nation she ever occupied. The USA would have a population of one billion people today and a GDP of $40 trillion.
I believe we need to use military force to eliminate the regimes engaged in tyranny, terrorism, and atrocity. Once those regimes are removed, we can rebuild those nations into first-world societies and incorporate them into the USA.
I believe the world can be united under the US Constitution, the Stars and Stripes, and the name of the United States of Terra.