Where It All Goes Down
Europe, 1848
The Communist Manifesto was published in 1848. Marx claims his analysis of class struggle explained "all hitherto existing society" (Section1.1)—in other words, all history up to and including 1848.
However, Engels writes in a footnote to the authorized English translation of 1888 that he and Karl mean all written history, since the pre-history of society was almost entirely unknown to them at the time of the original composition. That means the Manifesto was not meant to cover indigenous societies such as Native American tribes. Dudes Marx and Engels left a lot of stuff out—like the way our species governed itself for many tens of thousands of years.
Now, 1848 was a huge year for Europe. During this year, a whole slew of revolutions took place all over the continent, with the aim of establishing more democratic societies. These were not communist revolutions, and they mostly failed, but they showed how much political instability there really was under the surface all over Europe. It seemed as if the world was ready for change.
Similarly, the Manifesto is written as if Marx is talking about the whole globe. He says at one point that the bourgeoisie "must nestle everywhere, settle everywhere, establish connexions everywhere" (Section1.19). However, most of the manifesto actually focuses on Europe, especially Section 3, with its focus on rival socialist and communist authors, and Section 4, with its passages about other the communist relationship with political parties of the day.
As he wrote, Karl was especially aware that France was about to undergo a revolution. In fact, the Communist League, which commissioned the writing of the Manifesto, urged him to hurry up, because they wanted the document published in time to influence the political uprising. Some people think the rush is why the final section is so brief.