Well a group of people gather around to hunt for witches and at the end of almost every witch hunt if they catch the witched they burn them down.
Cultural, Ethnic, Religious, Linguistic Geographic nationalism is called Territorial Nationalism
Sea explorations were made by many countries centuries ago. These were headed by the European countries long back. The impulses or urges that influenced the explorers are to desire to take hold of other land for territorial expansion.
Another very important thing to consider as well was the trading. One country had to exchange products to another country. Hence, there were need for them to cross the seas.