This one requires some documentation.
Here are the best numbers I could find in Arabs killing Arabs since 1948, mostly relying on Wikipedia.
|War||Year started||Low estimate deaths||High estimate deaths|
|Algeria civil war||1954||150000||800000|
|North Yemen Civil War - Egypt||1962||100000||126000|
|Black September, Jordan||1970||2000||25000|
|Lebanese Civil War||1975||130000||250000|
|Libya Egypt war||1977||500||500|
|Iraq under Saddam||1979||600000||800000|
|Hama massacre, Syria||1982||17000||40000|
|South Yemen civil war||1986||10000||10000|
|Iraq invasion of Kuwait||1990||1000||2000|
|Yemen civil war||1994||7000||7000|
|Yemen - Sa'adah Insurgency||2004||5000||8300|
As you can see, estimates vary wildly for many of these events. I pretty much took the midpoints for the purposes of the chart, estimating about 1.5 million Arab deaths. (There have been perhaps 60,000 Arabs killed in all the Arab/Israeli wars combined including the intifadas.) I tried not to include Kurdish deaths nor those Arabs killed by the French during the Algerian war - much of that war was a civil war as well. I also did not include the Iran/Iraq war at all since that was not Arab on Arab violence, and Muslim on Muslim deaths is an entirely different set of numbers.