In the 20th Century there were actually 231 million deaths from conflicts of all types.
Of that number 12,804,500 can easily be identified as caused by Islamic rebellions or Muslim run Countries.
That would be 5.5 percent of all war related deaths directly atributed to Islam or Muslim policies.
http://www.cissm.umd.edu/papers/files/deathswarsconflictsjune52006.pdf
The table begins on page 73 I believe. The total is available on page 3 I think.
The table does not include anything before 1945 so the number is actually higher. Neither WW1 or WW2 should be counted as Islamic or Muslim caused deaths, BUT Turkey and the Armenia would as would the Philippines and other areas that are predominately Islamic.
Of particular note is this table only covers 41 million deaths from approximately 1945 to 2000. When one factors in that number the rounded up 13 million caused by Islam is rather more significant.