Because Japan is an island, the most common theory is that people migrated from the mainland from areas such as China and Korea. This combined with contact with those two places led to major Chinese and Korean influences. Throughout early Japanese history, there were many different periods where different rulers took power, all with very different ruling styles. The link below goes into more extensive detail on each of the major parts of ancient Japanese history.
Because of such strong Chinese and Korean influences, Japan played a major part in the spread of Buddhism. Also women were allowed to read and write, which led to many great stories being written, such as The Tale of Genji, which was considered to be the world's first full novel.
The link below gives a detailed list of the rulers of early Japan, as well as a description of each of the different time periods.