The Bronze Age of any culture refers to a time period when…
...the most advanced metalworking (...systematic and widespread use) in that culture used bronze.
The Korean Bronze Age had been thought to have begun sometime around 1500-1000 BCE, in Korea. Recent archeological discoveries indicate that it may have started as early as 2500 BCE. Bronze implements have been found (daggers and weaponry, for instance); it also seems that the Korea Bronze Age was more advanced than had been known before. The possession of bronze was a symbol of status within this culture.
The bronze daggers lent prestige and authority to the personages who wielded and were buried with them.
While many sources still look to 1500 BCE as the "generally accepted" beginning of Korea's Bronze Age, bronze production did not come into its own in Korea until much later.
...Bronze metallurgy does not become widespread until...around the 4th century BCE.
During the wars between different regions of China...
...migrating Altaic tribes entered Korea.
With this surge of people also came more sophisticated farming practices, with evidence of rice "cultivation" and the production of red pottery (as yet, lacking painted designs). Eventually, "engineering" advancements were seen.
Around 300 BC, iron was introduced and the first evidence of the underground ondol heating system.
Also—though first seen in China—there is also proof of the construction of more than one walled city. While it seems that these cities were first built in China, this custom spread as far as Taedong River in North Korea; one city there was known for many years as Old Chosen (Gojoseon), mentioned in historical Chinese documents.
lts people were known to the Chinese as the Dongyi or "eastern barbarians" or "eastern bowmen."
Old Chosen was the oldest and strongest walled city in the region, remaining so for many years.