Excerpts from Books and Wikipedia
"The kingdoms of Scotland and England were individual sovereign states, with their own parliaments, judiciaries, and laws, though both were ruled by James in personal union. James was the son of Mary, Queen of Scots, and a great-great-grandson of Henry VII, King of England and Lord of Ireland, positioning him to eventually accede to all three thrones. James succeeded to the Scottish throne at the age of thirteen months, after his mother was compelled to abdicate in his favour. Four different regents governed during his minority, which ended officially in 1578, though he did not gain full control of his government until 1583. In 1603, he succeeded the last Tudor monarch of England and Ireland, Elizabeth I, who died childless. He continued to reign in all three kingdoms for 22 years, a period known after him as the Jacobean era, until his death. After the Union of the Crowns, he based himself in England (…) from 1603, only returning to Scotland once in 1617, and styled himself "King of Great Britain and Ireland". He was a major advocate of a single parliament for England and Scotland. In his reign, the Plantation of Ulster and British colonisation of the Americas began." [Wikipedia]