Complex sentence: Vladimir adopted the "nom de guerre" of "Lenin" in December 1901, possibly taking the River Lena as a basis, publishing the political pamphlet "What Is to Be Done?" under this pseudonym in 1902.
Split into simpler sentences: Vladimir adopted the "nom de guerre" of "Lenin" in December 1901, possibly taking the River Lena as a basis,. He published a political pamphlet "What Is to Be Done?" under the "Lenin" pseudonym in 1902.