What is the most important event in Welsh history?

This is a matter for debate, and some would argue that certain events were more important than others. In reality, it's impossible to say, but probably the four most important events in Welsh history were the Plantagenet conquest of Wales under Edward 1st after the slaying of Prince Llewellyn the Great in 1285, the Glyndwr Rebellion of 1400, which temporarily re-established Wales as an independent nation for a decade until it was crushed by Prince Hal (later Edward 5th) in 1410, the Act of Union signed by English King Henry 8th in 1536 which officially abolished Wales as a separate nation and made it a part of England up until it's official Disestablishment again in Edwardian times, and the more generalised 'Welsh Revival', which began in mid-Victorian times and lasted up until shortly before the outbreak of WW1. This latter was a period during which the Welsh people began to rediscover their sense of nationhood and separate identity, resulting in a huge upsurge in national pride and a demand to be taken seriously by the British Government. It was led to a large extent by the Welsh religious revival, with prominent and respected ecclesiastical Welsh figures preaching the importance of Welsh identity to their congregations in churches and chapels alike across the Welsh nation. This led to the Disestablishment of the Church of Wales in 1920, and effectively began the process of Wales's re-emergence as a recognised entity once again, and it's being 'placed on the map' in both national and international public consciousness- it sowed the seeds of change that have led to the position Wales is in today, with a devolved law-making administration and a Nationalist party with MPs in the Westminster Parliament.