U.S. stock index futures fell on Wednesday, with S&P e-minis at a more than two-month low, on worries of an escalation of the conflict in Ukraine and as key merger and acquisition deals fell through. NATO said Wednesday Russia has amassed around 20,000 combat-ready troops on Ukraine’s eastern border and could use the pretext of a humanitarian or peace-keeping mission to invade. Rupert Murdoch’s Twenty-First Century Fox pulled its $80 billion offer to buy Time Warner Inc that would have created one of the world’s largest media conglomerates.