What does the word connive mean in this context? [closed]

"Connive" has two related, yet distinct meanings.

The most common meaning is to deliberately conspire to cause something to happen, eg "they connived to take over the business" would mean planning or conspiring to take over a business perhaps by foul means.

The secondary meaning though is simply to tacitly approve of something - to allow something to happen without actually causing it. Interestingly this is the meaning perhaps closest to the root meaning of the word which comes from the Latin conniver meaning "to close eyes to".

In your example, it is clear that the entire world clearly didn't cause or plan for Lincoln's death. The inference then is clearly that they turned a blind eye to, or ignored it.