Alright, I just made another graph.
http://img139.imageshack.us/img139/9154/image2kut.png
The red line is the total number of members in alliances in each round, using the primary Y-axis.
The blue line is the total number of active planets in each round, using the primary Y-axis.
The green line is the alliance limit of each round, using the secondary Y-axis.
The number of active players for r30 is missing, I did not have the information for that round.