A pebble? Not likely, and certainly not with the hyper low interest rate environment.
There were lots of rocks larger than pebbles over the last few years: China trade war with escalating tariffs, global trade anxiety, Trump political chaos (Russia and generally), impeachment, Middle East chaos, US / Iran, US / North Korea (daily, escalating threats of nuclear war), Brexit. None of them derailed the market from pushing higher.
It required a boulder precisely because of the interest rate environment. A pebble would not have done anything. China's economy just got put into the freezer for the past two months, the global economy is under serious threat, and even now the market remains very richly priced. It might yet require something even larger than a boulder to take this market down fully.
I think you may have a short memory. The international situation has never been very different qualitatively than it is today. Iran has been a mess for 50 years, much of that time far worse than now. We have been at war with north korea for 70 years, some of that with actual armies marching and shooting each other. In the 70s and 80s planes were being hijacked and bombed every week. Hundreds of thousands of people died from AIDS. All the while the economy was up, down, or indifferent to these things. The world is constantly in turmoil, listen to a billy joel song for more details.
There were lots of rocks larger than pebbles over the last few years: China trade war with escalating tariffs, global trade anxiety, Trump political chaos (Russia and generally), impeachment, Middle East chaos, US / Iran, US / North Korea (daily, escalating threats of nuclear war), Brexit. None of them derailed the market from pushing higher.
It required a boulder precisely because of the interest rate environment. A pebble would not have done anything. China's economy just got put into the freezer for the past two months, the global economy is under serious threat, and even now the market remains very richly priced. It might yet require something even larger than a boulder to take this market down fully.