- This question begins with an extremely strong claim: "since the start of the 20th century, the US has stepped in or started conflicts involving the direct use of military force mainly under presidents from the Democratic Party" - yet, there is no source presented for said claim. The lack of a source also prevents this claim from being quickly dismissed as lacking authority - consider how differently one would approach that question if it stated its claim was original work from its author.
- The statistics presented to back up the aforementioned claim are partial at best, and cherry-picked and intentionally misleading at worst - in this case the obvious omission of both the two Iraq, and Afghanistan conflicts. Yes, these conflicts are noted - but separately, below the provided partial data, and effectively as a single conflict rather than three.
- Continuing from the previous point, the partial statistics presented in the question immediately invite the reader to conclude that the answer to the question asked, namely "Is it true that the US has stepped into foreign conflicts mostly under Democratic presidents?" is "yes". This further invites to the reader to correlate the provided (partial) facts to conclude that the United States is more likely to go to war when lead by a Democratic president, implying that Democratic presidents are more likely to cause the United States to go to war.
- Regardless of all of the above, the political affiliation of American presidents with respect to their supposed warmongering, or lack thereof, is irrelevant as the Democratic and Republican parties have swung between majority liberal and conservative policies multiple times in their existences. Using "Democratic" or "Republican" in a historical context is thus meaningless, especially when attempting to correlate data. (This is to say nothing of geopolitical concerns, which muddy the waters even further.)
In short, not only is this question potentially misleading, it is also meaningless (as are any answers). As such, it provides no value and thus, in my opinion, should be closed.
More broadly, I believe that any and all questions posted to politics.se that make a claim(s), but fail to source said claim(s), should be immediately closed. A claim that is not sourced is a claim that cannot be verified, which invites discussion about the claim and its veracity as opposed to answers to the question posed - the former is a poor fit for the Stack Exchange Q&A format.
Particularly in an election year, particularly considering the partisanship in the United States at this time, I contend that the causative relationship it invites readers to draw is harmful and thus even more of a reason why the question should be closed. Especially since it's now showing up in Hot Network Questions.