1. Ancient Syracuse was not only one of the largest cities in the Greek world but managed to hold its own against the Delian League, Carthage, and even put up a good fight against Rome. I could see them expanding across Sicily and then some in another world if circumstances were a bit different.
2. Denmark-Norway could have probably had a larger colonial empire if they really put their backs on it, and generally focused less on the Baltics and Sweden. Of course, they would never get anything like the English or Spanish empires, but more trading posts across Africa, the Caribbean, and India seems doable.
3. Had Stephen played his cards better or just lived a bit longer then the Serbian Empire could have remained a powerful state in the Balkans, perhaps even keeping the Ottomans out of Europe.
4. Morocco was in a prime position to exploit the chaos of the 17th century and potentially nab some Iberian colonies in the Atlantic like the Canaries, and maybe even Northern Brazil. Similar to what the Dutch and English did alongside the Omanis and Ottomans. Unfortunately, they were stuck in a decades-long succession crisis and civil war so they never got the chance to IOTL.
5. Charlagmane not existing or him just not going on a campaign against the Avars could lead to them continuing to settle down and we get ourselves a Turkic or Slavic Pannonia.
6. Having the Ottomans collapse due to dynastic strife in the 17th century or be militarily toppled during the 19th, and we have an empire of similar borders but ruled by a new dynasty, likely the Girays in the former scenario and Muhammed Ali's in the latter.
7. Southen China is its own distinct entity from the north. This is already sorta the case IOTL but had the South remained independent for whatever reason, it's fairly likely it would have its own separate interests and ventures. Most likely it would be much more interested in naval and trade affairs, perhaps spreading Sinic culture to southeast Asia much sooner.