This landmass was attached to mainland Europe for eons, then the last Ice Age melted away (changing everything); new bodies of water formed including the English Channel and Irish Sea, Britain and Ireland were now islands and Stone Age settlers came ashore.
The Roman Legions (40,000 strong) crossed the dangerous English Channel in 43 AD. They eventually named this wild new province, Britannia. For some 350 years they controlled and influenced it, until their own Empire collapsed upon itself in 410 AD.
Britannia was now unprotected, and for the next 300 years invaders came from all directions. The Anglo-Saxons from Germany proved the dominant group, and a series of small kingdoms developed. One faction were called Engle, and from that name came "England."
Viking raids, though very persistent, were continually squashed. Then, in 1066, the Normans sailed in from France. William of Normandy was victorious at the Battle of Hastings, Harold, the last Anglo-Saxon king was now dead, and William was crowned William the Conqueror at Westminster in London.
During the so-called Middle Ages that followed, the Normans built hilltop castles and repeatedly tried to control Scotland and Wales, with little success. They introduced feudalism, where the king shares power with local nobles, who in turn allow common people (now the Anglo-Saxons) to farm their land.
For the next few centuries western Europe and England were certainly in turmoil; an out-of-control plague (Black Death) killed millions, competing royal families waged war, and the Hundred Years' War, pitting English kings against the French throne was debilitating.
The Tudor Renaissance followed a century of peace and stability, except of course in the many marriages of Henry VIII. To solve his divorce problems he split with the Catholic Church, formed the Church of England, and declared himself its leader.
Henry VIII's love of ships inspired the beginnings of English sea power, and in 1588, the English navy engaged and destroyed the mighty Spanish fleet. This overwhelming victory catapulted England into naval supremacy for the next three centuries.
Civil war raged in the mid-17th century as monarchy and Parliament supporters struggled for power. It led to the execution (beheading) of King Charles I. This created the Commonwealth of England, disastrously led by Oliver Cromwell. His dictator-like tendencies and 1649 punitive expedition into Ireland brought Parliament to its senses, and they finally restored a Monarchy, albeit one with now limited powers.
With the Acts of Union in 1707, England and Scotland merged and became the Kingdom of Great Britain. In the early 18th century, Great Britain quite successfully expanded its influence around the globe; from colonies in upstart America and the Caribbean islands, to significant power bases in Australia, Canada and India.