Yes, not necessarily after every sentence especially if the sentences deal with the very same thing and this is a very long article. Every paragraph should have one though. If you look at the chapter "Battle of Tampere" for example, the first three paragraphs have no citations but the last two have. If it's the case that that they've simply been split up to smaller paragraphs, we could use the same citation at several places with text  + .
I'm not criticizing the work done on this article, I'm just worried because I want to let it stay as FA-class. I think part of the problem could be that the article might be getting too long. For such a general presentation on the war, not every section has to be very exact. It makes citating harder and some of the chapters look really long which doesn't make them look too attractive to read. As film directors say, it is as important to decide what to leave out as it is important what to put in. Do you think the article might have got too long on some parts? '