Excerpts from Books and Wikipedia
"The Konoe cabinet's professed reason for the entry of the army and navy into northern Indochina was to complete the encirclement of China--if possible through diplomatic agreement with French officials in Hanoi or with the pro-Nazi regime in Vichy France, but if necessary by the use of force. The real reason was to prepare bases and concentrate troops and ships for eventually striking farther south at the surrounding countries rich in oil, rubber, tin, and the resources needed for self -sufficiency in the age of total war. . . . No war was declared, but Japan had now expanded its war in China by definitely stepping into World War II." [Hirohito, p. 379]