Where are you getting your data from?
There’s definitely a trend that extends since well before Trump (I recommend the book Surreptitious mentions), so tying this in any way to Trump is pretty misleading. It’s a long-term institutional success, not a personal victory.
The question to ask is, is Trump doing more to perpetuate/accelerate the existing trend, or is he doing more to stop or reverse it? Is he strengthening international institutions like the UN, international trade, and multilateral treaties? Is he strengthening domestic institutions? Is he helping the global and domestic economy to grow? Is he advancing cultural values of tolerance, respect, and peaceful conflict resolution?
In my view, undermining the UN, failing to check Russia, pulling out of TPP and starting a trade war with China, and ending the Iran nuclear deal are all moves that tend to increase the likelihood of international war. Weakening US institutions by eroding norms and failing to guarantee electoral integrity increase the likelihood of domestic violent conflict. And undermining tolerance, respect, and peaceful conflict resolution are likely to increase individual violence, as well as to reinforce the other two points.
But arguably his economic policies have been good for long-term growth, which is pretty strongly correlated with peace. The stock market has done well under him, and that might be attributable to his support for tax cuts and his dismantling of regulatory oversight, which could have been a net drag on the economy. If true, it’s hard to say if this outweighs the factors above, but it could. His effect on the international economy is likely to be worse, but I believe the recent boom has not been limited to the US.
Ultimately, his personal effect on the long term trend is likely to be very small. I tend to think it will increase violence relative to the counterfactual where someone else is president, because I think institutions and the stability they afford are very big factors, and that short-term growth won’t amount to much without stabilizing institutions to prevent much more costly setbacks. But I also think that the regulatory burden was too large for many industries, and it could be that the recent returns are actually attributable to this administration’s changes, and that they will compound going forward to improve total global wealth, and that that increase will compound and perpetuate peace even more going forward.