Final answer:
The significant Mickey Mouse cartoon that included synchronized sound and marked a turning point in animation was titled 'Steamboat Willie.' It followed the success of 'The Jazz Singer,' the first talkie, and propelled Mickey Mouse to international fame.
Step-by-step explanation:
The cartoon that changed everything by including sound and made Mickey Mouse an international icon was titled Steamboat Willie. Released in 1928, it showcased synchronized sound in animation, a technical achievement that followed the first 'talkie' The Jazz Singer from 1927, starring Al Jolson. Before the advent of sound in cinema, silent movie stars like Rudolph Valentino and Clara Bow captivated audiences, but Mickey Mouse's synchronized audiovisual experience in Steamboat Willie set a new standard for the medium and propelled Walt Disney's character to massive popularity.