For some off-beat analysis, a comparison of different periods of European consolidation. Just eyeballing the maps, it looks like the 3rd Reich was able to consolidate a bit more than the 4th. Still, considering Hitler was using tanks and Merkel is only armed with the power of persuasion, it's pretty impressive how much of Europe modern Germany "controls."
Eurozone member states
German Occupation in WW2
For reference, here's what Napoleon accomplished:
Of course, the most impressive empire has to be the Roman, if for no other reason than that no one came close to consolidating Europe to the extent they did for another 1500 years.