Well he was requesting better assurances that Ukraine would not join nato and that there be less build up of nato forces near Russians borders but he was ignored repeatedly. Russia clearly felt threatened and now it has led to this.
LOL as if those were the real issues here... If you believe he felt threatened by the build up of NATO forces (there were a grand total of 4 battle groups sent to the Balkans after 2014 to try to deter any little green men - Russia in recent days surrounded Ukraine with like 120+ battel groups!) I have a bridge to sell you!