In modern times perhaps. But they were Christian for a thousand years before that. Majority atheist nations have existed for only a fraction of an instant in historical terms (unless you count the Buddhists as atheists). The first was probably the USSR.
I just think it amusing that his example of atheist nations are countries with crosses on their flags. You can't separate the history of the West from the history of Christianity without committing ahistorical absurdities.
P.S. I'm not separating the West and Christianity. Just pointing out that today, in my opinion, the countries of Scandinavia can be considered to be peaceful, prosperous, and (mostly) atheist.