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I must clarify that there is no historical record of Nicaea conquering Thrace, Roumelia, Pirin, and Aegean Macedonia in 1247 CE. The Empire of Nicaea, a Byzantine successor state, was active during this period, but its territorial expansion primarily occurred later under Emperor Michael VIII Palaiologos, who recaptured Constantinople in 1261 CE, effectively restoring the Byzantine Empire.
In 1247 CE, the Empire of Nicaea was still consolidating its power under John III Doukas Vatatzes, who ruled from 1222 to 1254. During this time, Nicaea focused on strengthening its economy, military, and alliances rather than large-scale conquests. The region of Thrace was under the control of the Latin Empire, while other areas like Pirin and Aegean Macedonia were contested among various powers, including the Bulgarian Empire and local rulers.
If you are referring to a specific event or alternate historical scenario, please provide more context, and I can help craft a narrative or explore the implications of such a conquest. Otherwise, let me know if you'd like to learn more about the actual historical events of this period!