  Let $G\cong \mathbb Z/m_1\mathbb Z\times\ldots\times \mathbb Z/m_r\mathbb Z$
be a finite abelian group with $m_1\mid\ldots\mid m_r=\exp(G)$. The Kemperman
Structure Theorem characterizes all subsets $A,\,B\subseteq G$ satisfying
$|A+B|<|A|+|B|$ and has been extended to cover the case when $|A+B|\leq
|A|+|B|$. Utilizing these results, we provide a precise structural description
of all finite subsets $A\subseteq G$ with $|nA|\leq (|A|+1)n-3$ when $n\geq 3$
(also when $G$ is infinite), in which case many of the pathological
possibilities from the case $n=2$ vanish, particularly for large $n\geq
\exp(G)-1$. The structural description is combined with other arguments to
generalize a subsequence sum result of Olson asserting that a sequence $S$ of
terms from $G$ having length $|S|\geq 2|G|-1$ must either have every element of
$G$ representable as a sum of $|G|$-terms from $S$ or else have all but
$|G/H|-2$ of its terms lying in a common $H$-coset for some $H\leq G$. We show
that the much weaker hypothesis $|S|\geq |G|+\exp(G)$ suffices to obtain a
nearly identical conclusion, where for the case $H$ is trivial we must allow
all but $|G/H|-1$ terms of $S$ to be from the same $H$-coset. The bound on
$|S|$ is improved for several classes of groups $G$, yielding optimal lower
bounds for $|S|$. We also generalize Olson's result for $|G|$-term subsums to
an analogous one for $n$-term subsums when $n\geq \exp(G)$, with the bound
likewise improved for several special classes of groups. This improves previous
generalizations of Olson's result, with the bounds for $n$ optimal.
