marriage with a foreigner.
Is xenogamy popular in your country?
Marital - Marriage between people from different backgrounds - especially from foreign lands (or in fiction, from alien worlds); a more extreme/diverse form of heterogamy.
Botany - Floral fertilisation by genetically different pollen.
Origin: From Greek "xenos" (stranger) and "gamos" (marriage).
The United Nations finally legalised xenogamy, once they realised that the alien race wanted to coexist in peace.