Why has there been proposals to expand the number of permanent members on the UN Security Council?What are the reasons for and against doing this...

The United Nations was formed in 1945, immediately
following World War II in hopes of avoiding future such wars.  The victors, the Allied
powers, each received a seat on the Permanent Security Council and an important perk
that came with it: veto power.

In the modern day, Japan and
Germany are democracies and major trading partners with us and the rest of the world, so
they can make a credible claim that the world's second largest economy (Japan) and
largest economy in Europe (Germany) deserve a seat at the same
table.

The problem is, since the current members have veto
power, they can simply veto any proposal to change the current makeup of the Security
Council.  Russia doesn't particularly like Germany and China does not particularly like
Japan, and so their membership has always been vetoed or threatened with veto.  Why
should they vote yes when it diminishes their own power and
influence? 

Another  reason it could cause problems is that
with two new vetoes on board, it would be even more difficult for the UN to get anything
done, when it's already pretty difficult now.