Europe in 1972 was not the Europe that exists today; it was still a bunch of little countries that had been trying to kill each other a generation earlier. There was new money every hundred miles, and new cops and officials to give that money to: Europe was a collection of borders with countries separating them.
It was also farther away, and expensive to reach in any medium. Air mail required a whole different set of tools than regular mail: obscure stamps and special envelopes with red-and-blue wainscoting and see-through paper to save on weight. You could not call Europe. I mean, you could if someone else was paying for it, but if the bill was in your name, you could not call Europe.
In 1972, the Grateful Dead didn’t play any shows in Germany.