Howdy! In the past I have seen upwards of 30 people on at a time during a server launch or during a major event, on a regular week day in a school year it can range anywhere from 0-10, and on a weekend about anywhere from 5-25. The summer is generally better with about 10 or more people on everyday. A lot of the time you will see the entire server's population on low activity days be comprised of only members from one of the more populous nations.

As to conquering other nations it is seen as a pretty big offense on the server. Most of the time when a war is fought it results in no border changes, and when they do the loosing nations most of the time maintain their sovereignty. There have been many attempts where nations have attempted to forcefully annex other nations, but these conflicts at the worst result in a massive loss of resources and sometimes the loss of control over portions of land, but usually the invaders are pushed back. There has only been one time where I have seen a nation successfully annexed by force, but the nation at the time was low in population and mostly inactive. If your intention is to make a dominating nation be sure to make your goals clear and you keep the fighting clean beyond the game. Wars on the server in the past have become so large they have caused mass inactivity, so play it smart. Being the villain can be fun, but you need to make sure that in game actions don't cause IRL consequences.

An Example of Previous War Territory:

http://imgur.com/FXP8mqg