Complex sentence: While in the United States, Dvořák wrote his two most successful orchestral works: the Symphony "From the New World", which spread his reputation worldwide, and his Cello Concerto, one of the most highly regarded of all cello concerti.
Split into simpler sentences: While in the United States, Dvořák wrote his two most successful orchestral works. His Cello Concerto is one of the most highly regarded of all cello concerti.