The Truman Doctrine arose from a speech delivered by President Truman before a joint session of Congress on March 12, 1947.
Positive First. When installing a mower battery, always connect the positive cable first. The positive cable is red. It attaches to the battery terminal post marked with a plus sign, the letter P or the word POS. Attach the negative cable last. The negative cable is black.
The reason why you connect the battery cables to the dead car battery first is because you have 3 metal cable ends dangling and potentially touching metal car parts, thus a dead battery is less likely to cause any sparking since it has little or no voltage. That is the safest starting point for your jumper cables.