In 1867, Twain journeyed to New York City to lecture.  He soon departed for a Grand Tour of Europe and the Middle East, the experiences of which were recorded in his first book, The Innocents Abroad (1869).  The next two decades were the high point of his literary career, during which he produced Roughing It (1872), The Adventures of Tom Sawyer (1876), A Tramp Abroad (1880), The Prince and the Pauper (1882), Life on the Mississippi (1883), The Adventures of Huckleberry Finn (1884), and A Connecticut in King Arthur's Court (1889).  Among notable later works is Pudd'nhead Wilson (1894), a critique of racism in the post-Civil War South.

Since 1866, Twain had been lecturing to audiences across America and, occasionally, in Europe, usually on humorous topics at lyceums or after formal dinners.  In his later years, though, he used his celebrity status to speak out forcefully on social and political issues.  As a long-time critic of American and European imperialism, Twain wrote an essay in 1905, entitled "King Leopold's Soliloquy," to generate support for the American wing of the English Congo Reform Association.  The Harper Brothers firm, Twain's contracted publisher, refused to run the essay in their periodicals, Harper's Monthly and Harper's Weekly, but allowed its publication in pamphlet form by the American Congo Reform Association.  Combined with Harper's rejection of an earlier anti-imperialist essay, Twain concluded that he was being censored. 

In the 1870s, explorations of the vast Congo region of Africa's interior enticed King Leopold II of Belgium to establish a committee of European investors to oversee development of trade in the area.  They claimed that treaties with native African tribes gave them the authority to govern the region.  In 1884-1885, the Belgium army defeated a combined British and Portuguese force to establish the Congo Free State, with Leopold as its ruler.  He extended his control militarily during the 1890s.  

Leopold's administration of the Congo was exceedingly harsh, relying on slave labor to work the land's highly profitable rubber, ivory, and palm oil industries.  (In the cartoon, notice the "dividends" in Leopold's back pocket.)  The African workers were often mutilated as punishment for minor offenses.  It has been estimated that four to eight million Congo natives died as a result of the brutality of Leopold's regime.  Protestant missionaries initially alerted the outside world to the atrocities, and the Congo Reform Association was formed in 1904.

While in England in 1907 to accept the honorary degree, Twain reiterated his complaints against the inhumanity of Leopold's reign in the Congo.  Finally succumbing to worldwide pressure, the colony of the Belgium Congo was established in 1908 under the administrative oversight of the Belgium parliament.  The king retained some authority, but it became constitutional rather than personal.

The other subject of this cartoon refers to Twain's essay, "Christian Science and the Book of Mrs. Eddy," in which he claimed that Mary Baker Eddy did not write Science and Health, the founding text of Christian Science.  In 1903, he criticized Eddy as a liar and swindler, provoking the Century Theatre Club in New York City to replace him as master of ceremonies at their Actors' Fund Fair.  In 1906, Twain agreed to write an introduction for Livingston Wright's book, which also claimed that Mrs. Eddy was not the author of Science and Health.