What was the main country that Rome could not take over in the original Europe?

The main country that Rome could not take over in the original Europe is Germany. The Roman Empire made significant efforts to expand its territory into this region, but it faced formidable resistance from various Germanic tribes. The geography of Germany, characterized by dense forests and rivers, complicated military campaigns. Tribes such as the Cherusci, led by Arminius, achieved notable victories against Roman legions, including the famous Battle of the Teutoburg Forest in 9 CE, where three Roman legions were decisively defeated. This defeat effectively halted Roman expansion into Germania and established a strong sense of resistance among the Germanic tribes.

While Rome was able to exert influence over regions like Italy, Greece, and Britain—albeit with varying degrees of control and integration—Germany's fierce tribal structure and the challenging terrain proved to be insurmountable obstacles to complete Roman conquest. The Roman inability to establish lasting dominance in Germany significantly shaped the political landscape of Europe in subsequent centuries.