Emails may take up the bulk of our correspondence these days, but there was a time when a handwritten letter carried a considerable amount of weight—far more than the paper it was composed on. Take a look at five letters that had a demonstrable and powerful effect on world history.

1. The letter that prompted Abraham Lincoln to grow a beard.

In 1860, Abraham Lincoln was the Republican candidate for president. He was also clean-shaven, a look in stark contrast to the images and portrayals of a fully-bearded president that would endure well past his presidency. Growing a beard was a suggestion famously put forth by an 11-year-old girl named Grace Bedell, who offered some unsolicited campaign advice. In her letter to Lincoln that year, she stated that his face, which she described as “so thin,” would benefit from a beard because “all the ladies like whiskers.”

Lincoln wrote her back just days later and wondered if a beard wouldn’t seem like a “piece of silly affectation” since he had never grown one before. Despite the apprehension, Lincoln did grow a beard—perhaps the most famous one in American history. On the way to his 1861 inauguration, he arranged to make a stop in Bedell’s hometown of Westfield, New York, to let her know he had taken her advice to heart.

2. The letter from Albert Einstein that started the Atomic Age.

It would have been impossible for Albert Einstein to understand the gravity of his words as he signed a letter dated August 2, 1939, and later remitted to President Franklin Delano Roosevelt. In it, he alerted the president to work being conducted by scientists such as Enrico Fermi and Leo Szilard that may one day soon result in a “nuclear chain reaction in a large mass of uranium.” The consequences of such an achievement, Einstein wrote, would be “extremely powerful bombs of a new type.”

Einstein’s motivation was to communicate the potential of a superweapon to the United States government—one that could conceivably be developed by Germany first if the U.S. did not act. When Roosevelt received the letter, he told his military advisor, General Edwin Watson, to take action.

That wasn’t the only correspondence between Szilard and Roosevelt. Upon receipt of the initial letter, Roosevelt also promised to fund Szilard’s research into nuclear fission. When those funds were late in coming, Szilard wrote the president again and threatened to publish a paper he'd written that detailed some of the information needed to make a nuclear weapon—unless Roosevelt made good on his promise. Szilard got his wish, though he later expressed regret at the wheels he had put into motion, fearing a nuclear war would be catastrophic.

Collectively, the letters set into motion a chain of events leading to the Manhattan Project and the development of the atomic bomb, which was deployed in Hiroshima and Nagasaki in 1945 and helped bring an end to World War II.

3. The letter from George Washington that won the American Revolution.

George Washington had a problem. The Commander-in-Chief of the Continental Army was in the midst of a struggle that saw the American colonies trying to separate themselves from Great Britain. It wasn’t going well: The British Army had captured the New York City port and was advancing every day. Washington believed he could benefit from the assistance of a spy in the city to report on what was going on behind enemy lines. When he failed to rouse any volunteers beyond an inexperienced young man named Nathan Hale—who was captured and hanged in just under two weeks—Washington wrote a letter to a proven operative named Nathaniel Sackett.

Washington offered Sackett $50 a month to develop a network of spies and a system of espionage that could gather intelligence. Although Sackett didn’t make much progress, another operative, Benjamin Tallmadge, did. His Culper Spy Ring successfully gathered information about British troop movement and plans and had it delivered to Washington. British plans were continually breached, and General Cornwallis surrendered in 1781.

4. The letter from a mother that helped give women the right to vote.

In 1920, the fate of women’s suffrage rested in the hands of a man who was publicly opposed to the movement. On August 18 of that year, Tennessee House Representative Harry Thomas Burn cast the deciding vote on whether his state would ratify the 19th Amendment. Tennessee became the 36th state to do so, cementing the three-fourths of states needed in order to grant women the right to vote. His vote in favor was unexpected, as Burn was wearing the red rose that was the symbol of anti-suffragists. Just that morning a local newspaper had run an ad imploring people to “wear a red rose” to help defeat the amendment, “the most important issue that has confronted the South since the Civil War.”

When the amendment finally came up for a vote after prolonged discussion, Burn surprised observers by voting in favor of it. The reason? In his jacket pocket was a letter from his mother, Febb Ensminger Burn, that urged him to side with the cause of women’s suffrage. “Don’t forget to be a good boy,” she admonished. Burn later said that “a mother’s advice is always safest for a boy to follow.”

5. The letter that influenced the Civil Rights Movement.

When civil rights leader Martin Luther King Jr. was jailed in Birmingham, Alabama, on April 12, 1963 for participating in a march without a permit, he did not use the time to sit idle. Instead, King used whatever materials he could—including the margins of newspapers and paper provided by his lawyer—and spent the week he was locked up formulating an eloquent and measured response to criticism from the local clergy that protests weren’t the answer. By April 16, he had composed what would become known as the “Letter from a Birmingham Jail,” a lengthy rebuttal [PDF] that reinforced the need for public demonstrations against segregation.

In the letter, King argued passionately against the idea of waiting patiently for social change to be enacted. “Injustice anywhere is a threat to justice everywhere,” King wrote. The piece, which was later published in The Atlantic as well as King’s own book, 1964’s Why We Can’t Wait, was viewed as a rallying cry for activism during a crucial period in history and as documentation of the movement itself.