|This page in a nutshell: Don't indiscriminately add excessive references to an article in the hope that weight of numbers will prevent it from being deleted.|
Bombardment is the placement of a large number of references in an article in hopes that this will prevent it from ever getting deleted. But is it really safe? If you look at a number of AfD debates over time, you will see a variety of reasons articles get proposed for deletion, reasons going far beyond the lack of notability or references, while pages without references are kept.
Wikipedia's notability guidelines state that a subject is notable if there are multiple reliable sources independent of the subject. This suggests that an article bristling with sources should be safe. However, not all sources are equally valuable. A source may be reliable, but only cover a subject in a trivial manner, and if a subject is covered only by trivial mentions then it may not be notable no matter how many of them there are (see WP:BASIC).
For example, single events may be given bursts of news coverage in hundreds of newspapers around the world, prompting hundreds of news articles published on a single day. From the next day, not a single news source can be found.
Even if coverage continues for a period of time, local interests are not always viewed as encyclopedic.
Overloading an article with dubious and tangential citations can rebound when the article is nominated for deletion. Reviewing editors may not be prepared to look at all one hundred citations. They may instead choose to look at just a smaller sample. If they find only unreliable sources or sources that do not discuss the subject in depth they could then recommend deletion. The two genuinely supporting sources may be entirely missed.
What is and is not bombardment
Adding additional references is good when each source has a lot of information of its own. Since one of the purposes of references is to provide the reader information beyond what the Wikipedia article says, providing more sources of information is a good thing. However, adding a reference to already verified material merely to get the reference into the article is not a good practice. Such material is better placed in a "Further reading" section.
Use of the same source to verify different information in different parts of an article may be necessary. But when this occurs, it is still a single source. Such citations can all be made to point to the same reference in the references list by using the named references system. This avoids the reader being bombarded with a long list of references that are all really the same source.
When the sources are identical to one another or otherwise redundant, on the other hand, this can be seen as bombardment. News agencies like the Associated Press share their stories with many other news organizations. Many news sites then present the exact story, word-for-word. The only difference is the URL used to access the same information. Instead of "multiple, reliable sources," these are merely a single source.