Why did the Romans successfully conquer territories earlier? But in the 1st century they were defeated?

We are talking about the battle in the Teutonburg forest in the territory of modern West Germany near the Rhine. The Roman army, quite large for that time (three legions plus cavalry), were lured by the Germanic tribes and defeated, after which the expansion in this direction ceased. The border of the Roman Empire passed along the Rhine, where they built fortifications – limes. However, this defeat did not end the expansion altogether. It lasted until 117 AD (the death of Emperor Trajan) – to Britain, Dacia (now Romania) and Mesopotamia (now – Iraq).