Why did Theodore Roosevelt prepare for military action in the Philippines?

When war erupted, Theodore Roosevelt was an Assistant Secretary of the Navy, but as his boss was out of the office, he immediately took action on it. After this, he sent a telegram to the admiral that if war was coming, he would take offensive action against Philippines because it was a big part of the Spain's Empire. Then a few days after that, war was started. Roosevelt did was the telegram was told and Philippines was captured showing the intense force of the U. S. over Spain.

When the actual president of the United States, William McKinley, died, Roosevelt take his place, he was now known as a hero.