Amit is absolutely right. But some points to think about:
1. The most naïve thought is like this: Coke is a global brand. Coke is being consumed in all the countries. All coke country managers advertise Coke. That means that you can get ad dollars in every country in the world.
2. I heard that Google is monetizing really well in Eastern Europe.
3. We have seen ad networks emerge all across the world now, the problem is that you need to partner with each one independently to start monetizing.
4. Clearly, the US is a much more mature region with higher CPCs/CPMs. However the competition is also crazy
5. UK is the #1 country in means of monetization (All companies say that…)
6. One final comment: It is now agreed that you can create a $1bn consumer internet company in Germany alone.

Bottom line: International is an opportunity but hard work.