What this cartoon tells us is that Americans in 1921 (or at least the cartoonist) felt that there were simply too many Europeans wanting to come to the United States. The cartoonist is arguing that “the only way to handle it” is to reduce the number of people being allowed to come.
We should be sure that we do not necessarily take one cartoon to represent American public opinion at a given time. A cartoonist can have an opinion that is not held by most Americans. However, in this case, the cartoonist’s opinion was actually congruent with what Congress did to restrict immigration. Therefore, we can safely assume that many Americans agreed with the cartoonist.
In the cartoon, we see huge numbers of Europeans wanting to come to the United States. This is shown by the size of the funnel’s upper opening. We can also see that the cartoonist wants to dramatically narrow the opening that lets the immigrants into the US. This is represented by the “Uncle Sam” figure putting in the “3% gate” to reduce the size of the lower end of the funnel. From this, we can learn that Americans felt there was too much immigration and that the number of immigrants allowed into the US should be reduced.
This is exactly what Congress did in 1921. It introduced a law saying that each European country could send a number of immigrants to the US that was equal to 3% of the number of people in the USin 1910 who had been born in that country.