Tehran continues to deny its involvement in Yemen’s civil war, but there is no doubt it has become the main force behind the Houthi rebels, supplying them with materiel, military advisers, and perhaps manpower as well. And Moscow, much as it does in Syria, is aiding the Islamic Republic in these efforts. Micky Aharonson and Yossi Mansharof write:
Iranian activity [in Yemen] depends on cooperation with Russia, which protects [Iran] against unfavorable UN Security Council resolutions and enables [it] to continue exporting terrorism there [and] to extend its hold and influence in that country. Among other things, Russia makes it possible for Iran to foster the deadly terrorist attacks committed by the Houthis and their missile barrages aimed at Saudi Arabia, [which supports the government that the Houthis seek to overthrow].
After having been in contact with Russia a number of times since 2015, a Houthi delegation met with the Russian deputy foreign minister Mikhail Bogdanov. The Houthis then declared that Russia should be involved in any settlement in Yemen. In 2018, the Houthis sent President Putin a letter calling on Russia to intervene in the war. Russia’s widely reported willingness to conduct a dialogue with the Houthis provides them with an international platform for voicing their demands. It also establishes Russia as an international patron of relevance to events in Yemen. . . .
To summarize, Yemen is another focus of instability in the Middle East. This instability, ostensibly a result of internal tensions, is exacerbated by external countries: both those in the region, like Iran, and more remote ones, like Russia. . . . One result of the cooperation [between the two] is the arming of groups that are inflicting horrendous damage on the people of Yemen. The result may be that the capabilities and interests of external players, such as Iran and Russia, in continuing their military and economic support for the parties in the conflict may be of more importance in determining its outcome than are the parties themselves.