well that still leaves Warlords as the primary empire builders. Reliance on Charisma or Intelligence with strong motivation and ability to lead others.
Technically Fey Warlocks could do it as well but completely lack the mindset to build and sustain a country. A PC might manage it, but it should be rare.
Hmm Starlocks may be in the running as well, how is that for a scary world - one where nations rise and fall on the whims of the insane stars.
Paladins may attiain high rank, but with Intelligence as their universal dump stat, nations run by paladins will suffer many problems.