"A Modern History of the Republic of Korea: From 1870's and Onwards"
Written by Daniel Kim, a history professor at Seoul University.
Chapter 1: Intervention in Asia
There is dispute over what happened next. Apparently, the ship's crew seized Adjutant-General Yi and his two deputies, who were attempting to pursue a small boat launched from General Sherman with six men attempting to reach shore. According to Governor Park's report, another government official, Shin Tae-jung, tried to persuade the crew to release Yi Hyon-ik and his men but failed. Instead, the General Sherman moved upstream, firing cannons and eventually anchored at Hwang-gang-jung (House of Yellow River). Governor Park later reported that the ship had fired her guns into the crowd, killing seven and wounding five. Then, five men launched a boat and navigating north of Pyongyang to determine the river's depth. The citizens of Pyongyang gathered on the riverbank, shouting for the release of Yi Hyon-ik. A man in the boat (probably Robert J. Thomas, the only one who spoke Korean) replied they would give the answer if they were allowed inside Pyongyang city. The crowd started throwing stones at the small boat. Korean soldiers shot arrows and guns at the launch, which retreated back to the ship. The Koreans sent a rescue party and managed to free Yi, but his deputies (Yoo Soon-won and Park Chi-young) were killed. The ship eventually turned back and sailed down until she ran aground into Yang-Gak island, an island across from Pyongyang.
Fighting continued for the four days, after which the Koreans resorted to fire boats, filled with wood, sulphur and saltpeter. The first two failed to inflict any damage, but the third set General Sherman afire. Unable to stem the flames, the crew jumped into the water.
According to the Korean Official historical record, "Kojong-silrok" (Vol.3), there were two survivors from the initial attack, Robert Thomas and Cho Neung-bong. However, they too were beaten to death.
In January 1867 the USS Wachusett (1861) (under Captain Robert W. Schufeldt) attempted to investigate the demise of the General Sherman and successfully arrived in Joseon, demanding information. The Joseon government, afraid of the Americans, admitted that they had destroyed the boat. [1]. However, the Joseon government refused to take responsibility for their actions and demanded America to repay Joseon for "intruding in Joseon's rightful territory and attempting to invade." Outraged, the American captain turned back towards the United States and reported everything to the U.S. government. By 1869, the United States was outraged at the Joseon government for committing an "act" of war and asked the assistance of the French for intervention against the Korean government. France, having multiple missionaries and such die in Joseon due to persecution, agrees to help America take down the isolated and hostile country. Both countries used the attack on their ships and people as an act of war, though both didn't formally declare war and called it a "war of liberation."
On June 1st of 1870, the American and French government sent about 2,000 marines along with a fleet of 50 ships to Joseon's capital of Hanyang. As a result, a firefight ensued between the obsolete Joseon Army and the allied forces of America and France. Due to the backwards army doctrine and weapons of the Joseon Military, the allied forces scored a huge victory, killing nearly 40,000 Joseon soldiers at the cost of 200 allied marines. Only 1 ship, the USS Shenandoah [2], was sunk while Joseon's nearly nonexistent navy (of 14 small wooden ships) and coastal batteries (numbering at around 300-500) were all destroyed within hours. As a result, the Joseon government capitulated after the rapid fall of Hanyang and surrendered to the allies on June 10th of 1870. Regent Heungseon Daewongun and his loyalists fled to China, where they vowed to return and re-establish the monarchy. However the First Republic of Korea was established the day after the Hanyang Treaty was signed. This new republic was administered by the Americans and French and elections would soon follow later that year.
At first, the American people are quite against the idea of "annexing" territory. However, President Grant assured the nation that the America was "freeing the Korean people from a backwards and mindless government." It was revealed to the populace later that Korea would NOT become a territory, but in fact a republic. When the populace learned of this, it acted favorably towards the government and supported the establishment of a democratic ally in Asia. America's economy would soon benefit shorthand with the newly opened trade with Korea. Because of the trade with Korea, America would ignore Japan (except a few trade agreements) and focus on expanding their markets in the friendly Korea.
Of course, China objected to the "violent occupation of the Korean people." Influenced by the monarchy loyalists, the Chinese government claimed that America and France was attempting to annex the Korean people and oppress them. However, the intentions and goals of France and America was clear after merchants flocked to the Korean Peninsula for trade and such, revealing a relatively modernizing nation with a fairly happy people. Thus, the outrages and screams of "colonialism" from China was vastly ignored by other powers. Instead, the other major powers began to compete in the Korean markets to sell goods and such in exchange for raw resources which Korea apparently had plenty of.
Within Korea, many Korean people were unsure of how to react. The oppressive monarchy was removed from power and the Korean people were now benefiting from world trade and French-American support. However, the Korean people weren't entirely free and despite the new republic, heavily dependet on France and America. Despite the ambivalent thoughts, the Korean people reacted well to the American-French dominated Korea and became a stable democracy. The country would remain on friendly terms with France and US for many years to come and expand their economy to become a major economy and contender in international affairs.
Though unknown at the time, Korea would later play a huge role in international affairs... Changing the flow of history...
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[1]: The PoD of this timeline is when the USS Wachusett actually arrives on time. In OTL, the ship turns back due to a bad storm and another ship comes to inquire Joseon of the USS Sherman. However, by then, the ship's sinking is old news and doesn't get too much attention. Here, the public is aware that a backwards nation attempted to destroy a U.S. vessel, leading to a bigger reaction than the 1871 expedition to Joseon.
[2]: Ironically, this was the vessel that was sent to investigate the Sherman sinking after the first ship in OTL.
*Note: It is plausible that America would work with France in this situation. While not exactly friends, the French was pissed that Korea kept on executing it's missionaries and even attack Korea in 1867. On the flip side, America also attacked Korea in 1871 in order to take a shot at gunboat diplomacy (which would fail). Although unlikely, the two countries working together to remove the hostile Korea government is not all that implausible. As France was entering 1870, it was facing multiple problems with the populace. As a result, Emperor Napoleon could have worked with the Americans in order to a) put himself in a favorable light to the world and the populace and b) profit by opening trade with the Koreans. America, on the other hand, was looking to expand it's influence upon Asia and Korea would fit ITL. Based off of this, I allowed America and France to work together to take over the Joseon government, which was weak and ineffective at the time.