Before northern Europeans and what the Romans loosely called barbarians were introduced to christianity?

you're right: those concepts were introduced in nordern europe with force and then upheld with pressure by the roman church.. but you're wrong about the concept of "tribal structure" in ancient german people: their nuclear family and fidelity were much strongest than roman ones..just read Tacitus and his Germania. You will be really amazed to see how important was the family amidst German tribes. No divorces, almost absent unfaithfullness, in opposition to the dissoluteness of roman customs. The turning falls with the cristianity: what was in the nordern traditions is now imposed by the church, and ual encounters are now only to make children, not even for love. The next step happens with luteran reform: north europe separate from roman church, the remaining catholic countries, nearer they are to rome, the most they follow the pope's law and order..and Italy, as popedom head office has one of the lowest devorce rate, but also an outdated ual mentality.