Most states have a history of voting for a particular party and the presidential candidates will count on their votes again. This leaves a handful of states where the election will be decided. These are the election battlegrounds.
Presidential elections are run using an electoral college. Each state is given a number of votes based on its population. This means some states are worth much more than others.
For example, California (population 37.7m) has 55 votes, while a more rural state like Montana (population 1m) has only three votes. The presidential candidate who wins in a state wins all that state's college votes.
Published by BBC