You need to add more context for that to mean anything. For example...
He was upset over the replacing of his favorite chair.
In this example "over" is defining the subject that the person is upset about.
Question...What is he upset over?
Answer...The replacing of his chair.
To replace means to exchange one thing for another thing. "We are replacing the window because it has a crack in it".
Here, the structure is "start X over Y". It means thst Y is the reason for X.
--The children started fighting over the toy (=they both wanted the toy, so they fought for it)
--Bob started moaning over the amount of work he needed to do (=he needed to do a lot of work, and that made im sad, so he started moaning).
They started a campaign over the replacing of Ms P.S.M. Charles with a retired Navy officer=Ms. PS.M. Charles was replaced by a navy officer, and the customs officers didn't like that, so they started a campaign. The campaign has cost 12 billion rupees so far.
Thumping=surprisingly large [old British slang]