Marrying an American is one way to be allowed to emigrate to the United States, obtain permanent residence status and start the citizenship application process.
Some other ways, for those who qualify, are refugee visas, some types of work visas, trying your luck with the visa lottery, etc .
As to being easier, speaking from my experience of adopting our first son abroad and years later bringing my foreign fiancee and her children here, the work involved in the processes themselves seem to be about the same.
Of course in order to gain American citizenship through marriage, a few conditions have to be met:
First - you have to be single and legally free to marry
Second - you have to find an American citizen to fall in love with and who wants to marry you
Third - the citizen who plans to marry you has to prove that he or she is financially capable of supporting you and any children you will be bringing with you. This includes signing affidavits swearing that neither you nor your children will apply for public assistance for a specified number of years.
Fourth - you have to pass a physical exam and undergo a background check showing no criminal past.
Finally, the first and second items above are critical in that you not only have to be legally free to marry but also seriously intend to enter into an enduring marriage. Sham marriages solely for the intent of gaining entry into the U.S. or gaining citizenship are illegal.
I hope this is of help to you.