The Master System, originally sold as the Sega Mark III in Japan, was redesigned and sold as Sega's first home console in North American. The system could play with both cartridges and the credit card-sized "Sega Cards", which retailed at lower prices than cartridges but had lower storage capacity. It was released on June 1st 1986 for $200.00, which would equate to $457.62 today.
Unable to find the specific date of release, but source point to sometime in June of 1986 for it's North American release.
June 1st, 1986 Source: giantbomb.com
Released sometime in June it included a multi-cart with the games Hang-On and Safari Hunt.