This link of the twentieth century battles has various estimates of casualties, and suggests that maybe "only" 750 thousand died...and that doesn't include the deaths of the seige of Leningrad or other 20th century battles.
The battle took place between 23 August 1942 and 2 February 1943 and was marked by constant close-quarters combat and lack of regard for military and civilian casualties. It is among the bloodiest battles in the history of warfare, with the higher estimates of combined casualties amounting to nearly two million
The unprecedented scale of the two world wars becomes apparent when we realize that even small pieces of them killed more than most of the other complete wars of the Century. Even more horrific, World War II's Russian Front produced 13 of the century's 15 bloodiest battles all by itself. (The siege of Leningrad alone could rank as the 20th Century's 12th worst atrocity once civilian deaths are added in.) In fact, part of why this list so long is that I wanted to get far enough down to show some other wars as well.at least they note:
* Manila, Philippines (massacre of civilians by Japanese: Nov. 1944-Feb. 1945): 100 000
- Gilbert, History of the Twentieth Century: 100,000 Filipinos k.
- William Manchester, American Caesar (1978): "nearly 100,000 Filipinos were murdered by the Japanese"
- PBS: "100,000 of its citizens died."
But the Japanese atrocities during their retreat explains the atrocities against the Japanese soldiers who were not allowed to surrender but fled to northern Luzon, another unreported stories.
On December 15, 1944, landings against minimal resistance were made on the southern beaches of the island of Mindoro, a key location in the planned Lingayen Gulf operations, in support of major landings scheduled on Luzon. On January 9, 1945, on the south shore of Lingayen Gulf on the western coast of Luzon, General Krueger's Sixth Army landed his first units. Almost 175,000 men followed across the twenty-mile (32 km) beachhead within a few days. With heavy air support, Army units pushed inland, taking Clark Field, 40 miles (64 km) northwest of Manila, in the last week of January.
A military history of those days can be found HERE.
another version HERE. PBS version HERE.
most of the criticism againt MacArthur seems to be that he should have just bypassed the Philippines and left their soldiers wander around killing folks instead of fighting for the islands, but his pride made him willing to fight to help the Filipine people instead of just isolating the Japanese here and getting on with the battle for Japan. And the intrepid PBS site faults MacArthur for hurrying to Manila and not giving Yamashita a way to escape. So they headed into the mountains.
a Filipino side of the story here.