The central conflict in this novel is defined by the pursuit of the white whale, Moby Dick. Other conflicts are developed and resolved over the course of the book, but Ahab's pursuit of the whale takes precedence over all of them.
It is this conflict that reaches its climax at the end of the novel. The resolution of this conflict determines the "fate" of most of the characters in the book - Captain Ahab, Queequeg and Ishmael and the rest of the crew.
On the third day, with Ahab’s harpoon in his hump, the white whale turns toward the ship itself and, with a powerful blow of his forehead, sinks the Pequod with all the crew still on board.
Ishmael is the sole survivor of the adventure, surviving by sheer luck to narrate the tale of Ahab and the white whale to the reader.
The conflict represented by the pursuit of Moby Dick is clearly the most important conflict in the novel, as evidenced by its function in the narrative (forming a through-line that connects all other episodes of the book and driving the book forward, constituting the context for the book's major themes, and, in its resolution, concluding the story climatically).
Additionally, many of the novel's minor conflicts arise from the larger one of pursuing the whale. The disputes and dangers faced by the crew are part of the business of whaling, to some extent, but are multiplied as the journey becomes defined by revenge.
In pursuing the white whale, many elements of the adventure become charged with symbolic meaning.
Viewing the Pequod’s voyage as a metaphor for life, the book seems to be saying that in following ambition or any far-off goal, an individual risks missing out on many of the good things in life, including home and domestic happiness.