How did the Korean War start?

The Soviet Union declared war on Japan, Korea's colonial ruler, in between the US nuclear strikes on Hiroshima and Nagasaki in August 1945, and sent troops pouring into the peninsula.

Washington and Moscow agreed to divide it into two occupied zones along the 38th parallel, and with the Cold War rivals unable to agree on a path to Korean independence, the split was enshrined in 1948 with the emergence of two rival states.

Both the Communist North and the capitalist South claimed to be the legitimate government of the entire peninsula.

On 25 June 1950, the North invaded the South as Kim Il Sung attempted to reunify it by force.

What happened next?

The Northern troops seized Seoul in three days. Multinational UN forces -- mainly American -- arrived in the South to help, but were pushed back to the Pusan Perimeter, a pocket in the southeast.

A bold counter-offensive launched by UN forces commander General Douglas MacArthur recaptured Seoul via the Incheon Landing, splitting the North's forces and turning the tide.

UN units swept north, nearing the Chinese border in October before Beijing reversed the war's course again by sending hundreds of thousands of troops to aid its faltering Communist ally.

Seoul fell to them again in January 1951 and was recaptured once more two months later - the fourth time the city had changed hands.

Another two years of attrition followed as the fighting wore its way to a stalemate.

How did the fighting end?

After more than two years of truce talks involving 158 meetings, an armistice was finally signed in July 1953 by North Korea, China and the US-led United Nations Command.

But South Korea's then-president Syngman Rhee, who still wanted to secure full reunification under Seoul's rule, refused to sign.

Up to three million Koreans died as a result of the conflict, along with 37,000 Americans.

Chinese casualty figures remain disputed but Western estimates commonly cite a figure of 400,000, while Chinese sources put it about 180,000.

Yet the Demilitarized Zone that divided the two countries after the fighting was little different to the 38th parallel.

Why is there no peace treaty?

Occasional skirmishes and incidents have continued between the two Koreas for decades.

Their leaders jointly pledged to seek a treaty following their summit in April, but the question of the North's nuclear weapons still hangs over the issue, which has multiple complications.

Both Pyongyang and Seoul continue to claim sovereignty over the whole Korean peninsula. A formal treaty could imply mutual recognition of each other -- something neither side has been willing to accept.

As a signatory to the armistice, Beijing has warned that any end-of-war declaration without its participation would be invalid.

The ambiguous nature of the original conflict is another complication. As neither the North nor the South acknowledged the other's existence, no formal declarations of war were made by either side.

The US referred to its intervention as a "police action," with the UN deeming North Korea's invasion "a breach of the peace." (AFP)