We hear frequently about abuse of the legal system here in the United States: frivolous lawsuits, folks who would rather sue than work their problems out like mature individuals, people suing the manufacturers of products that had little or nothing to do with the damages they suffered.
Have lawsuits increased in frequency over the years, and if so, what was the impetus for this increase? Was there some landmark decision that made filing a lawsuit easier and/or more lucrative?

Some blame it on a slow economy. See

I know this does not totally answer your question, but it’s a start.

The linked article seems to be more about lawsuits relating to contract disputes rather than the type of suit the OP is talking about.

I don’t know that there is a factual answer to the OP. I’m not aware of any decision that made it “easier or more lucrative” to sue. A number of decisions from SCOTUS have made it harder (and in some cases impossible) to sue. Some people blame the proliferation of law schools and by extension lawyers. The more lawyers there are, the more lawsuits will be filed as they seek clients. Some of the more high-profile frivolous suits (like the fast food suits) get a lot of press and may color the perception of suits that are filed which are completely legitimate but get a little tarred by the “frivolous” brush.

One aspect of the U.S. legal system that may give rise to more frivolous lawsuits is that the loser in most lawsuits is not automatically required to pay the legal expenses of the winner.

If we adopted a “loser pays” rule, it would certainly cut down on the number of suits filed, and would also reduce the number of instances of defendants settling suits simply to avoid the expense of dragging the dispute all the way through the courts.

The counter-argument, however, is that it would bar some worthy plaintiffs from seeking justice, since some plaintiffs wouldn’t be able to afford to take the risk of losing.

It may not be as severe a problem as you think. See A Nation Of Victims:

(Yeah, I know it’s an old article; I had a more recent one that said essentially the same thing, but I can’t find it now.)