Homeland defense doesn't generate any force requirements beyond having enough National Guard to save lives in natural disasters and to baby-sit nuclear power plants on Code Red days.
An economically confident America has - since becoming a world power at the start of the 20th century - tended toward global engagement. It is during times of economic stress (1930s, 1970s) that America has become more withdrawn.
Transnational terrorism, in the form of the Salafi Jihadist movement, is fundamentally a function of globalization.
Despite living in this post-9/11 age of transnational terrorism, the risk of death during air travel has plummeted to the point where we now measure it in the 'per billions' of passengers.
The Marines are like my West Highland Terrier. They get up every morning, they want to dig a hole, and they want to kill something.
Some Western demographers have posited, due to the female shortage created by the one-child policy, that China will be forced to field a vast force - as in tens of millions strong - of wifeless men who'll gladly wage wars around the planet to burn off all those unrequited hormones.
