The signifiers (symbols, etc.) in Daniel have been interpreted and reinterpreted over the years to refer to a vast array of different signifieds, to the detriment of the original logic of the book.
The statue dream incorporates the four kingdoms motif common in the Hellenistic era, and the original scheme of the book was: gold = Babylon, silver = Media, bronze = Persia, iron = Greece, divided iron/clay = the divided kingdom of the Seleucids and Ptolemies. Note especially how ch. 11 describes how Alexander the Great's kingdom (Greece) will be uprooted and given to others, split among his four generals and split into two kingdoms (the king of the north = Seleucids, the king of the south = Ptolemies), and the two kingdoms will attempt but fail to unify. The last king of the north (= little horn, =stern-faced king, etc.) is Antiochus Epiphanes, who did just the sort of thing described in Daniel.
However, God's kingdom failed to materialize after his downfall, and Judea came under the control of the Romans since 66 BC. As a result, the Median and Persian kingdoms were lumped together and the fourth kingdom came to be regarded as Rome. This interpretation can be found in the Dead Sea Scrolls and in the NT. Revelation also assumes that the last kingdom will be Rome (= Babylon the Great). But since the end of the Roman Empire failed to bring what was expected, things were reinterpreted again. Some lumped together Babylon-Medeo-Persia in order to make the fourth kingdom the Arabs, who followed the Romans in controlling Jerusalem. Others interpreted it (or the divided kingdom) as among the kingdoms that replaced the classic Roman empire: the Holy Roman Empire (= the Catholic church, for some Protestants), the French, etc. In the nineteenth century, the global extent of the British empire led many to identify that kingdom as the last one before the second coming. The JW teaching is a variant on this. But none of this has anything to do with the original logic of Daniel, which was entirely focused on the events of the Hellenistic period.