The Exploration of the Moon started when the Space Race/Space Age (1957 - 1969/1976) heated up and the Soviet Union and the United States both raced to the moon and later other planets. With the Space Race the world and technology changed, especially the interest of the moon.
The Soviet Union was the first country to land on the moon ( Without any Humans ) and the United States was behind in the space race but the United States was the first one to land with a human on the moon which started the exploration. More Satellites and Probes during and after the space race/space age were sent to explore the rocky surface and during the robots and human missions that successfully landed on the moon they found that the moon had craters and had a hard surface. But they also found dead volcanoes, and lava flowing through areas on the moon.