What is the main conflict and what is the Inciting Incident for the Main Conflict?

One main conflict is internal... Hiccup's lack of self-confidence, and in turn, the peoples' ack of self-confidence in him as their future leader. Hiccup physically does not measure up to the Viking standard, but his logic and problem solving skills make up for it.

The other conflict in the novel is that of man versus nature, namely man versus the dragons. After the baby dragons are grown and trained, Hiccup and the others pit them against Green Death, one of their own kind, and something dragons do not do. The inciting action being the dragons dropping feather bombs on Green Death.