If USA/Russia/China are the 3 most powerful countries, who are 4,5,6,7,8,9,10 ?

[kelestian]

In Brazil's place I'd put either Turkey, South Korea, and Saudi Arabia. Saudi Arabia is probably the best answer; its soft power has been enormous in the Muslim world for decades and its military is one of the best funded (and with its recent interventions probably among the most experienced top) in the world.

the country that even with billions of dollars spent on US toys can't beat a few thousand Yemeni tribesmen with dusty AKs? 

You can use that same logic against the US in Afghanistan

Saudites doing this conflict much worse, than Russia in Syria or US in Afghanistan. They can't conquer Houthis strongholds, even capital, they suffer huge losses in living force and vehicles etc.