This sounds very strange but it is true. A microbe changed the course of history in the UK. You see, in the early 1500s king Henry the 8th was Crowned king of England but he was not intended to be king. Henry had an older Brother called Arthur, when Arthur Tudor was 15 years old he was killed by a fever called English Sweating Sickness. It is not known what caused the disease but it is most likely to be a bacteria or virus, a Small microscopic lifeform that is too small to be seen with the eye.
King Henry the 8th was a very stubborn king and wanted to divorce Catherine, his wife because she didn't give birth to any male children. The church rejected his request so he changed the national religion of the united kingdom from Catholic to Protestant.
The Spanish refused to form an alliance with the English because they considered Protestants to be heretics. If you look at the bigger picture you would see that history would be very different because his older brother would be very unlikely to make the same decisions. A microbe made historical events different by killing the king of England and causing a different king to rule, a king that is considered by many to be very divisive.
