The USA

To fuel the continuity and prosperity of the US Industrial Military Complex, IMC, the US must always have an enemy to war on.
This means for the sake of the IMC the American nation will never ever know a century peace. A century of peace did take place in Western Civilization once. It was the Pax Romana of ancient Rome, 100 years of continuous peace under the Antonine Caesars. This list of Caesars ended with Marcus Aurelius.

The apparent current enemy, Islamic Jihadism, is not an actual physical enemy, It is an ideology, You cannot come up with greater and more powerful bombs, planes, nuclear submarines and aircraft carriers to exterminate an ideology. And the IMC 
desoerately needs to generate greater and more powerful bombs, planes, nuclear submarines and aircraft carriers to charge the American public purse for its dollar prosperity.

So the current search is for a real enemy that has meat and blood on it. 

It cannot be Russia because Trump is offering to the US a  new direction and approach in relating with Russia - buddy buddy friendship with Vladimir.

And it is not possible with China because China is all for TRADE, TRADE and more TRADE not WAR, WAR and WAR.

So, who might be viable enemy?

Amazingly, these are the three top candidates:
                                             1. Iran
                                             2. Saud Arabia
                                             3. Israel.

So, Go for it America! Take your choice.