Why is nitrogen gas relatively unreactive under ordinary conditions?

Nitrogen gas ($N_2$) is relatively unreactive under ordinary conditions primarily due to the exceptionally high strength of the triple bond that holds the two nitrogen atoms together.12

This bond, which involves the sharing of three pairs of electrons, has a very high bond energy of 226 kilocalories per mole. Because this bond is so stable, the activation energy required to initiate a chemical reaction with molecular nitrogen is extremely high, rendering the gas inert to most reagents under standard conditions. Furthermore, the high stability of the $N_2$ molecule contributes to the thermodynamic instability of many nitrogen compounds, as the bonds within those compounds are generally much weaker than the bond in molecular nitrogen.1