The development and evolution of the Samurai sword is closely tied to the different Japanese periods. The following paragraphs provide a condensed and comprehensive view of Japanese history.
ANCIENT PERIOD (Before AD 650)
Swords of this period were primarily made by Chinese and Korean masters. There aren't very many examples of these swords around today. This period marks the begining of the Japanese culture under the reign of emperor Jimmu.
NARA PERIOD (650 to 793)
The first capital city of Japan was established during this period. New laws were introduced and the imperial family established a stronghold. The need for a better equipped army started creating the need for the development of better swords.
HEIAN PERIOD (794 to 1191)
Kyoto became the capital of Japan and was ruled by the Fujirawa clan. This era produced some of the best examples of Samurai swords as new techniques were developed.
KAMAKURA PERIOD (1192 to 1336)
Feudal Japan is started. The Shogunate form of government is in place. The Mongols attempt to invade Japan and are met by Kamatura warriors who defend the island ferociously. However, their weapons are no match to the Mongol forces and are beaten. Suddenly, typhoon season starts and the mongol ships are destroyed stopping the invasion of Japan. The Kamakura warriors see the need for better swords and begin working on developing better techniques. Some of the best built swords emerge at this time. Emperor Godaigo gathers up forces and manages to overthrow the Shogunate.
MUROMACHI PERIOD (1337 to 1573)
The Shogunate returns to power. Japan is split in two as civil war erupts. The conflict lasts for over 100 years and causes a huge supply of swords to appear.
AZUCHI-MOMOYAMA PERIOD (1574 to 1602)
Japan is reunited. The existing large armies are put to use by invading China and Korea. The art of sword making continues to expand.