On June 25, 1950, a surprise attack by North Korean soldiers who crossed the 38th parallel easily overwhelmed South Korean forces. The United States leapt to the defense of the South. As South Korean, U.S. and U.N. forces fought back and gained ground into North Korea, Chinese forces joined the war on the North's side later that year. To this day, China remains a crucial ally of North Korea and the U.S. of South Korea.

What toll did the war take?

The toll of the war included about 1.2 million deaths in South Korea, 1 million deaths in North Korea, 36,500 deaths for U.S. troops and 600,000 deaths for Chinese soldiers.

What are the lasting effects of the war?

The brutal war separated thousands of families, and created the world's most heavily fortified border. It also drew the alliances that exist today.

When was the armistice signed?

The armistice was signed in July 1953.

What were its terms?

The terms of the armistice included the creation of the Demilitarized Zone, aheavily fortified 155-mile long (250 kilometers) 2.5-mile wide line separating the two countries.

How have relations between the North and South been since then?

In the last 60 years, diplomacy between North and South has zigzagged from conciliatory to bellicose.

During more friendly times, the two countries arranged emotional family reunions for those separated by the war in 2000, their leaders shook hands in a 2007 Pyongyang summit and ran freight trains across the border.

But periods of rapprochement have been counterpointed by flareups.

More recently, the North shelled the South Korean island of Yeonpyeong leaving two marines and two civilians dead. Pyongyang claimed Seoul provoked the 2010 attack by holding a military drill off their shared coast in the Yellow Sea.

That same year, North Korea was also accused of sinking a South Korean warship, killing more than 40 sailors.

Without an armistice, what can happen?

The two sides can resume hostilities if they so choose.

What are the risks of a military clash?

A military clash could risk drawing in the United States, which has about 28,500 troops stationed in South Korea as part of the security alliance between the two countries.