The kingdoms or realms that emerge after the Roman Empire, such as the Frankish and the Turkish, are smaller in size. In the later empires there is also a lot of internal strife that causes them to keep falling apart. Note that this time is spoken of in Daniel 2:44 as the time of the kingdoms or kings in the plural. There will always be discord and kingdoms will fall apart. This is also what is indicated by the feet and toes which are of iron mixed with soft clay. Kings and rulers will try to form great empires during this time. They will try to rule with harshness in such a way that they might actually accomplish this.
41 And as you saw the feet and toes, partly of potter’s clay and partly of iron, it shall be a divided kingdom, but some of the firmness of iron shall be in it, just as you saw iron mixed with the soft clay.