The best option from the list would be "battle" in terms of a category for "bombardment", since this refers to when an enemy launches weapons (usually bombs or missiles) into the territory of the enemy.
Because they were...........
1. All of Africa, excluding Abyssinia and Liberia, was conquered by European powers.
2. Through colonization and military conquest.
3. European powers needed the resources of Africa to supply their citizens and industries.
