At the second stage of the green card application process (filing from abroad with the National Visa Center), the sponsoring spouse must prove that they intend to establish a "domicile" in the United States either before or at the time of the foreign national spouse's arrival in the country.
Domicile is a complex concept and is evaluated on a case-by-case basis.
It is generally required (with a written explanation and supporting evidence) that the sponsoring spouse has taken concrete steps towards leaving the foreign country to live in the U.S. – such as changing a foreign address to establish a physical mailing address in the U.S. (by signing a lease, purchasing a home, or even making arrangements for housing with a friend or relative), leaving a foreign job and applying for jobs in the U.S., and opening a U.S. bank or investment accounts.
Learn more about domicile in this guide.