You may be aware that Saudi Arabia is leading a coalition against rebels in Yemen.
Saudi Arabia's air force has done the bulk of the bombing on civilians, much of which can be described as war crimes.
What isn't as well known is that the army invading Yemen isn't led by the Saudis, but by coalition partner the United Arab Emirates. That's where this story gets interesting.

The first thing to understand about the UAE army is that it is a mercenary army.

The Arab Organisation for Human Rights in the UK (AOHR) filed a complaint yesterday with the International Criminal Court (ICC) against the UAE’s alleged war crimes in Yemen. A press release from the organisation also accuses the UAE of engaging mercenaries to fight in Yemen, including nationals from Australia, South Africa, Columbia, El Salvador, Chile and Panama.
“The UAE did not want to get its own hands dirty, so it employed foreigners to do its dirty work,” said Me. Joseph Breham, an international criminal lawyer at French law firm ANCILE Avocats.

The most interesting thing about this army of mercenaries is where they were contracted from - R2.

The top officer in the Presidential Guard is an Australian citizen called Mike Hindmarsh, while responsibility for recruitment was delegated to a UAE firm called Reflex Responses Company, also known as R2.
R2 was founded in 2010 by a United States military contractor called Erik Prince, the same year the former US Navy SEAL officer moved to the UAE – and only months after he sold his stake in the ‘controversial’ mercenary firm, Blackwater.

Oh joy. Erik Prince again.
You can't turn over a rock in the middle east without finding that snake.
He's now an advisor in the Trump Administration.

Hold on, that isn't the whole story. Here's the plot twist.
The UAE is directly undermining the goals of the Saudis in the Yemen War.

Emirati security forces control the city of Aden, where the coalition has set up its improvised capital. This capital, however, is without a defined leader. The so-called internationally recognized president, Abdrabbuh Mansour Hadi, currently lives in Riyadh as a consequence of his failure to garner public support. If that weren’t enough, the Emiratis have now reportedly banned Hadi from even entering Aden.
In fact, Abu Dhabi has done just about everything possible to remove Saudi influence from southern Yemen altogether. Earlier this year, Yemeni politicians with long-term ties to the UAE formed the Southern Transitional Council behind Riyadh’s back to govern the south on their own terms. The UAE also fully supports south Yemen’s separatist movement, which directly conflicts with Saudi interests in Yemen.

The stated purpose of the Saudis is to put their puppet, Hadi, back into power.
But their coalition partner, UAE, not only has ruled out his return, but intends to make sure that Yemen doesn't even exist in its present form.
What's more, UAE appears to be seeking its own little empire.

Over the past summer, Abu Dhabi and Riyadh butted heads again over control of crucial Yemeni islands in the Bab al Mandeb strait. Whatever entity controls these waterways controls a significant portion of global trade.

With it now under U.S. and Emirati military occupation, Abu Dhabi’s goal was to create a new Yemeni province called Bab al Mandeb. This province would include the two Red Sea islands as well as Yemeni districts currently part of Hajj, Lahj, and Taiz provinces. Bab al Mandeb province would be under Aden’s control and ultimately the UAE’s. In other words, the Emiratis would control almost all of Yemen’s western coast, including port cities and Red Sea territories.

The UAE pushed Hadi and Riyadh to declare this new province, which they of course declined to do, likely due to the fact that this would increase UAE influence in the region while lessening Hadi’s (and Riyadh’s) already minimal power.

Perhaps most striking, however, is Abu Dhabi’s growing military might throughout the Horn of Africa. The UAE has used the war against Yemen as a springboard to secure its hegemony throughout the entire region.

In the past few years, Abu Dhabi has secured bases in Eritrea, Somaliland, Djibouti, and the semi-autonomous region of Puntland.

The UAE is so bold that they even contemplated using their army of mercs to invade Qatar.