Hello Adam,
The general consensus in the Amillennial (or
present millennium) school is that the beast from the sea (Rev 13:1-9) at the time John wrote, is Rome—the military/political entity that persecutes the saints—and that the beast from the land (Rev 13:11ff.) signified the false teachings or philosophies supporting the first beast. The second beast is also referred to as the false prophet (Rev 16:13; 19:20; 20:10).
The original WCF, from 1646, states,
There is no other head of the Church but the Lord Jesus Christ. Nor can the pope of Rome, in any sense, be head thereof, but is that Antichrist, the man of sin, and son of perdition, that exalteth himself, in the church, against Christ and all that is called God” (art. 25.6).
The 1689 London Baptist Confession, at 26.4, follows the older 1646 WCF.
The American version of the Westminster Confession, however (used by the PCA and OPC), omits the second half of the second sentence:
There is no other head of the Church but the Lord Jesus Christ. Nor can the pope of Rome, in any sense, be head thereof.
The pope loomed large in the 1600s and 1700s, whereas now that is not the case, or so it appears at the moment, though the papacy does indeed bear close watching.
Back to the two beasts: the contemporary amils view any Christian-persecuting governments since John wrote as continuing manifestations of the beast, and all false teachers supporting these beast entities as recapitulations of the second beast or false prophet. Most of these amils anticipate a final manifestation of both the first and second beasts at the end of the last days, that is, at the time of Armageddon (the global war against the saints). The American Presbyterians wanted to leave room for other contenders for the title of a final antichrist, lest we be blind-sided by a limited focus only on Rome.
It is understood by some that the final Babylonian empire—generally understood as the entire world system against God and His people—has a headquarters nation, even as the Babylonian empire of Chaldea had its headquarters (the vast city of Babylon) and the Roman Empire had hers (the city-state of Rome). The American Empire which militarily, economically, and culturally dominates most of the world (though it is in decline now) is seen by some amils as the present headquarters nation of latter-day Babylon.
I attach a paper on the topic fleshing out this viewpoint,
The Fate of Babylon:
A Study in Determining the Identity and Demise of Babylon in John’s Apocalypse: