The world map has been, in historical terms, pretty darn stable over the last forty years. There have been a few late instances of decolonization, of course, and the relatively orderly fracturing of the USSR and Czechoslovakia into their constituent parts, as well as the disorderly fracturing of Yugoslavia into its constituent parts. Eritrea calved off of Ethiopia. East Timor calved off of Indonesia. But on the whole, it would be a very recognizable world -- with very recognizable flags -- to someone who just arrived from 1970.
Go back another 28 years, though, and the situation changes dramatically. Here's the front cover of the "War Edition" of the Hammond's World Wide Atlas, from 1942.
And here's the back cover:
We're used to seeing a full complement of 200 countries, give or take, these days. In 1942, Hammond's could only drum up 48 independent countries -- and that including three that had already ceased to exist for the next fifty years, Estonia, Latvia, and Lithuania (although a few smaller countries, like Luxembourg, were left off).
Most of the flags on the chart, however, are still in use (although some look a little funny, because Hammond's showed the formal state flag instead of the more recognizable civil flag). Noteworthy exceptions include Canada, Germany (!), Egypt, and India (still a British colony here).