Defeat of the Spanish Armada

The UK didn't exist at that time. England, Scotland, Wales and Ireland were still completely separate countries which had not joined the United Kingdom yet; that only happened in 1707. It was only England which was at war with the Spanish Empire. As to why England won, let's just say that there was a lack of co-ordination between the Spanish army and navy, a reluctance on the part of the Spanish King to cancel the invasion when logistical problems started becoming serious, and the tactical superiority of the English Navy during the battle itself. It was a great turning point in European history - it marked the beginning of the decline of Spain and the rise of England (and later the UK).