On September 1, 1939, Nazi Germany sought to expand geographically; a year earlier, in September 1938, the powers France and England had negotiated for Czechoslovakia, an ally of the former, to cede the border regions known as the Sudetenland, at the express demand of the government of German Chancellor Adolf Hitler, who between 1935 and 1937 succeeded in getting the allies to accept the rearmament of the German nation.
In March 1938, the annexation of Austria to the III Reich announced Germany's intention to expand into Eastern Europe, likewise, the dismemberment of the Czechoslovakian state the following year announced the avalanche of a war of great proportions.
In its expansion intentions, the German nation signed a non-aggression pact with the Soviet Union in August 1939; for its part, in Western Europe, France, and England guaranteed the integrity of the Polish state in the face of what had happened in Czechoslovakia. The Russo-German agreement allowed Germany to invade Poland a month later without fear of a Soviet military response.
On September 1, 1939, the Germans launched their "blitzkrieg" against Poland; the speed and the German numerical and military superiority forced the Polish army to surrender; Warsaw, the seat of the Polish government, fell on September 27.
For their part, the Allies, firm in their position to guarantee the integrity of Poland and its government, declared war on Germany and by extension on the Axis countries on September 3, which formally started the Second World War.
While all this was happening in Europe, in Mexico the last year of the government of General Lázaro Cárdenas was beginning, who, in the context of the belligerent context and its expansion on an international scale, a year earlier had decided and negotiated the expropriation of the oil industry.
On September 4, 1939, Lázaro Cárdenas made public his neutrality resolution, using which our country abstained from getting involved in any way in the armed conflict; the then President of the Republic declared:
The entire Nation joins with me in deeply regretting the fact that a group of great States, for one circumstance or another, have resorted to armed struggle to seek the solution to their differences, thus superimposing violence on the rule of law and justice.
Given the existing state of war and to establish and make known the attitude of our country in the present conflict, the government over which I preside declares its resolution to remain neutral in the conflict, subjecting its conduct to the norms established by International Law and to the precepts contained in the treaties in force which determine the obligations of Mexico as well as those of the belligerents.
During the following three years in which the armed conflict developed on European soil, our country remained in total neutrality to the events that took place on the old continent. However, in February 1942, submarines of the German naval fleet began to sink merchant ships in the waters of the Gulf of Mexico.
Further north, towards the end of 1941, the Japanese bombing of the U.S. military base at Pearl Harbor in the Pacific Ocean led to the entry of the United States into the armed conflict; after that act, the American nation declared war on the Axis countries.
In this context, the captains of the German submarines warned the ships supplying oil to the United States that they would be attacked if they continued supplying the hydrocarbon.
Finally, on May 13, 1942, at 23:55 hours, the German submarine U-564 attacked the oil tanker "Potrero del Llano", which four days earlier had left the port of Tampico with a cargo of approximately 40,000 barrels of crude oil. Given this fact, the Mexican government -which in solidarity with the United States had already broken off relations with the Axis countries- sent a strong note of protest:
"If by next Thursday, the 21st of the current month, Mexico has not received from the country responsible for the aggression complete satisfaction, as well as guarantees that the indemnities for the damages suffered will be duly covered, the government will adopt the measures demanded by national honor."
Despite the protest note, the Mexican government did not receive any response, and, instead, another oil tanker "Faja de Oro" was torpedoed by another German submarine days later. Manuel Avila Camacho, President of the Republic, in a meeting with his entire cabinet and in an urgent session called before the Congress of the Union, on May 28, 1942, validated the decree by which, as of the 22nd of the same month, a state of war was declared between Mexico and the Axis powers.
As a consequence of the latter, on May 8, 1944, the participation of the 201st Squadron of the Mexican Air Force was announced, to face the war.
Source: Legislative Museum