I'm going to make a prediction about the event that starts "Civil War" and, mind you, these are just predictions!
From all of the analysis of the first trailer I've seen, I've begun to notice a few particular things which could pertain to the inciting event of the MCU's Civil War. First, you notice that something being blown up towards the beginning. To me, this looks like the U.N. The second shot that comes into play from the trailer is when the armed guards are storming a compound where you assume is where Bucky is. In that shot, you may notice armed guards lying dead as Crossbones and his crew come in. Here's what I think is the beginning of and what causes the MCU's Civil War: that U.N-looking place in the trailer is actually some council room in Wakanda, presumably where World Leaders are invited to meet, under the leadership of, first T'Chaka and, then, T'Challa.
This is, what I believe, is where Crossbones and his team are. Here they plant the bomb, all while implicating Bucky and then, trapping him where we find him at the beginning of the trailer. This is why, later in the trailer, you see predominantly Black Panther fighting Bucky and chasing after him; because he thinks that Bucky is responsible.
Lastly, notice that the "policemen" that are with Crossbones have the German spelling of "police" (which is Polizei) on their jackets. Now, color me obvious...maybe, but could this be hinting at an alliance between Crossbones and Daniel Bruhl's character, Baron Zemo, which we know IS in Captain America: Civil War?