What does 之下 mean in 加上本来就对空心怀反感的贵族们煽动之下，发生了示威游行?
Answering in context of this edit:
In short
Yes, 之下 means &quot;under (the situation of) ...&quot;. A more common form is &quot;在...之下&quot;. For example:
在群众压力之下，他最後正式向公众道歉。
Under (the situation of) the pressure of the masses, he eventually made an official public apology.
Additional info
Since some comments have doubt with the grammatical aspect of the sentence, I would like to explain more.
The word 加上 indicates that something happened(有些事情发生了) in previous sentences alongside with the 贵族们煽动. To aid understanding the sentence easier let's try to omit the part 本来就对空心怀反感的 and add 有些事情发生了 at the start. The sentence becomes:
有些事情发生了。加上贵族们煽动之下，发生了示威游行。
Which can be translated to:
Under the situation of (something happened) and the stir-up of the nobles, a march ensued.
A comment suggested that the sentence should be rewritten to either:
加上 (本来就对 空 心怀反感的) 贵族们煽动
(This rewrite removed the cause-effect relationship of the stir-up and the march, which diluted the meaning of the original sentence a bit.) or;
在 (本来就对 空 心怀反感的) 贵族们煽动 之下
This rewrite broken the concurrent relationship of the &quot;something happened&quot; part.
I think the two rewrites can actually be combined together to:
加上 在(本来就对 空 心怀反感的) 贵族们煽动 之下
Which retains both the meaning of 加上 and 之下.
Finally, frankly speaking the grammar of this sentence is not very good, especially the ending part . For me, I would rewrite the whole sentence as:
加上在本来就对空心怀反感的贵族们的煽动之下, 結果示威游行就爆发了。
And by reading more of the original text, it seems that the author is just doing &quot;literal&quot; translations, without much care about the relationship between sentences.