The Second Korean War (popularized name by the media), otherwise known as the Korean Continuation War or the War of Korean Aggression/Liberation, was an armed conflict between the People's Republic of Korea (North Korea) and the Republic of Korea (South Korea).
The official name for the conflict is the Second Korea War, or KWII/KW2. It was erroneously named the Second Korean War by the media, while in reality is was simply a three-month long skirmish on and around the border. Many people also called it the Korean Continuation War, seeing as the First Korean War never officially ended with a peace treaty. The people of Korea usually calls it the War of Korean Aggression in the South and they used to call it the War of Korean Liberation in the north.
The two countries of Korea has long been at each other's throats. North Korea under the delusional Kim regime has seen communism as the true way and has shunned the South for their ideology of capitalism. North Korea has also had a bitter relationship with the United States, referring to them as the 'American Empire' and threatening of nuclear war. During the 1950s, the Korean War happened, fought between North and South Korea as well as the United States and the People's Republic of China - the only communist/capitalist war between major world powers in history. During the 60 years of the bitter ceasefire agreement, both Koreas exchanged several bullets on either's side of the 38th Parallel.
However, turning it in for the worse was during the early stages of the 21st century. The United States had maintained a military presence in their South Korean ally's nest for over 60 years since the end of the first war. They were the one small wall standing between ceasefire and war between the two Koreas. South Korea grew restless, and when one too many provocations from the North happened, an unknown South Korean soldier returned fire which escalated into a full-blown battle between KPA and ROKA border guards. When the US arrived, the war began.
Course of the War
The first to make their move were, of course, the North, as Kim Jong-un and his generals ordered over one million poor conscripted soldiers to charge into the South's territory. Jong-un, having faith in his deceased father and their country, believed the capitalist enemies of the South and their overseas allies would soon be crushed by the power of the North's military might. One of the first major engagements in the war was when a KPA battalion of around 2,000 men attacked a USCM logistical outpost near the border. The staffer in the outpost, one Alexis Alexander, conducted a daring and dangerous attempt to hold them off until reinforcements could arrive. Using signal flares, decoys and what-not, Alexander and the Marines were able to hold the KPA battalion back until a battalion of US troops could surround them and annihilate them.
On another front, the United States R&D found themselves in a successful spot: The new M1A4 Paladin tank needed to be evaluated on the field should it be adopted by the Army and Marine Corps. An elite Marine tank regiment accepted to adopt the Paladin Tank and test it against the KPA. It turned out to be a huge success because even the most advanced North Korean tanks were no match for the technology and firepower of the Paladin. The communist tank divisions were forced to retreat, much to the chagrin of the North's leadership. Kim Jong-un ordered all who retreat to be executed for the incompetence, but the KPA officers didn't comply.
Believing their leader to be a delusional fool, a band of KPA generals moved into Pyongyang and removed Kim Jong-un from power, installing a successful 'heir' to the throne of North Korea. After several disastrous attacks for the KPA, North Korea sued the South for peace. The United States wanted the two Koreas to unite and end the bitter fighting, but what the South wanted the least was a unification with the Medieval northern state. Instead, all parties accepted an agreement on status quo ante-Bellum, the way things were before.
The United States and South Korea were the most organized of the three contenders in the fight. The US deployed around ten regiments of Marine, Navy and Air Force while some special forces groups like the Army Rangers and Delta Force were deployed to aid the conflict. South Korea deployed all their available manpower in the Army, Navy, Air Force and Marine Corps, around 800,000 infantrymen in total. Backed with the US contributions the South had a standing army about the same size of that of North Korea.
North Korea, however, deployed whatever manpower they could find, from both the armed forces and the civilian population. Many civilians were pushed into combat, several of which were even unarmed. This created sparks in the population and they began to torment the North Korean government, which was one of the reasons the KPA generals disposed of Kim Jong-un. The other reason is that Jong-un had nearly no sense of military strategy: The whole North Korean battle plan was to storm the South's defenses and hope for a breach. They lost many soldiers that way, but the total losses have never been disclosed by either the military government or the later Unified Korean Republic.
The aftermath of the conflict was brief if not nonexistent. However, a major effect the war had on the world was associated with the Chinese. Officially not an ally to North Korea since their agreement faded away during the Cultural Revolution, the Chinese found themselves in a political feud instead. With the Mudanjiang Disaster of 2014 and dissidents in Xinjiang, the Party Government was bickering on about different solutions for their problems. With the escalation of the crisis in Korea, several hardline elements of the PLA decided to take the shot and did a daring invasion of the Republic of China, the Taiwan Conflict.
The new military government in North Korea also remained in power for nearly 15 years, until the American retreat of 2028 saw South Korea without a proper ally, so the North took the liberty and finished what their predecessors began; the Third Korean War.