So it seemed to us. It was an agreeable and therefore a readily acceptable idea. We imagined the Franco-German War of 1870-71 and the Russo-Turkish War of 1877-78 were the final conflicts between Great Powers, that now there was a Balance of Power sufficiently stable to make further major warfare impracticable. A Triple Alliance faced a Dual Alliance and neither had much reason for attacking the other. We believed war was shrinking to mere expeditionary affairs on the outskirts of our civilisation, a sort of frontier police business.
-The New World Order by HH. G. WELLS
I do not understand what did the author mean by "expeditionary affairs" and "frontier police business".
According to Cambridge dictionary "expeditionary unit" means :
a group of soldiers sent to another country to fight in a war
And about "frontier police" I am confused.
As a verb police is (Cambridge dictionary): to control or guard a public event or area by using members of the police or a similar force.
But also it has a meaning as a noun. I don't know which one to choose.