How were the Articles of Confederation and the Constitution similar?

There really were not very many similarities at all
between the Articles of Confederation and the Constitution that replaced them.  The
people who wrote the Constitution were so unhappy with the way things were under the
Articles that they changed most things about the
government.

The only truly important similarity is that
both documents set up democratic systems of government.  This was a truly important
thing at the time because it was very different from any other form of government.  Both
documents explicitly went away from monarchy, which was the most prevalent system at the
time.

In addition, both documents set up governments that
were in some ways limited.  They both set up systems in which governments were not
allowed to do certain things.  This was an important idea at a time when governments
tended to be able to do whatever they wanted.

There were a
few other similarities, like the fact that the states are not allowed to conduct foreign
policy under either document.  But these similarities are very minor.  The only major
similarity is that both documents create systems in which there are democratically
elected limited governments.