1] The Gita was written in the 1st century AD -Buddhist sutras were at least 1st century BC -- and a lot older.
2] Buddha was not an atheist and Buddhist scriptures are FULL OF REFERENCES TO GOD, GODS AND CELESTIAL BUDDHAS. Full of such references.
3] Mahabharatha initially did not have Gita as part of it - it was a later addition.
4] Mahabharatha was written in 2nd century BCE after Buddha.
5] Buddhism was still the main religion until Islam, came and burned Nalanda and killed every Budhist in the worst genocide in history.
6] Everything in the Gita has been written in Buddhist scriptures but unless you study them you will not know. Also Buddha does talk about duty and defense - do not follow Sei Lankan or Western Buddhist sources on the internet but READ THE BUDDHIST SCRIPTURES THEMSELVES.
Edit: There is NO atheism in Buddhism and ANY SCHOLAR will tell you the Gita was a recent addition. The Mahabharatha is NOT the Gita and Vyasa was a contemporary of Mahayana authors. You have NOT read Buddhist scriptures to say Buddhism is atheistic and so I will not debate you. Also, Hinayana is NOT older than Mahayana - modern Buddhist scholars reject this notion. Hinayana scriptures also are full of references to God and even that Buddha is Brahman. I will not waste my time as I know you are NOT A PHD IN RELIGION via your response,
Edit 2: Adi Shankara was a prachuani Buddhist or hidden Buddhist who said Lord Buddha was the Supreme of the Kali Yuga FYI. You are clearly a student, I am an author and will not waste time. Do your homework my friend. :)
EDIT 3: BUDDHA SAYS HE IS GOD IN MANY SUTRAS IN BOTH HINAYANA AND MAHAYANA DOCTRINES. YOUR LINK IS LAUGHABLE. VYASA WROTE THE MAHABHARATHA AND VYASA LIVED IN 2ND CENTURY BCE. OR DO YOU NOW BELIEVE VYASA LIVED IN 3300 BCE??? ALSO, BUDDHA SPEAKS OF MANY PREVIOUS BUDDHAS THAT GO BACK TO THE BEGINNING OF TIME. BUDDHA IS FAR SUPERIOR TO HINDU GODS. HINDUS BELIEVE IN SATI OR WIDOW BURNING, CASTE SYSTEM AND CHILD MARRIAGE. BUDDHA CORRECTED YOU ALL. BUDDHIST NATIONS LIKE JAPAN ARE FAR MORE CIVILIZED THAN HINDU INDIA FOR A REASON.
EDIT 4: STEPHEN KNAPP SAYS KRISHNA BALARAM COINS ARE 2ND CENTURY BCE - CHECK YOUR OWN LINK!!!!!!!!
Ancient Krsna Balaram Coins 200 BC
Krsna, Agathocles coin,
Ai Khanoum, Afghanistan, 2nd century B.C.
http://www.gosai.com/chaitanya/sastra-vedas/agathocles-krishna.jpg
A lot of numismatic evidence also corroborates the antiquity of Krishna. For instance, excavations at Ai-Khanum, along the border of Afghanistan and the Soviet Union, conducted by P. Bernard and a French archeological expedition, unearthed six rectangular bronze coins issued by the Indo-Greek ruler Agathocles (180?-?165 BC). The coins had script written in both Greek and Brahmi and, most interestingly, show an image of Vishnu, or Vasudeva, carrying a Chakra and a pear-shaped vase, or conchshell, which are two of the four main sacred symbols of God in Vaisnavism. Many other finds of ancient coins also prove the antiquity of Krishna worship in India.
Balarama, Agathocles coin,
Ai Khanoum, Afghanistan, 2nd century B.C.
http://www.gosai.com/chaitanya/sastra-vedas/agathocles-balarama.jpg