Theravada and Mahayana - The Crucial Differences I struggle with the idea that Buddhism has two warring schools and wonder why they cannot make peace. 

What are the issues on which Theravada and Mahayana cannot agree? 

Just bullet points would be fine. I'm not inviting an argument about who is right, just asking for the facts. A summary of key doctrinal differences is what I'm after, if this is possible. 

Issues such as which scriptures are authentic may be omitted since this is not a doctrinal difference, but differences in the interpretation of those scriptures would have to be included.   

Thanks.

EDIT: Thanks for all the answers. They make fascinating reading. The question has been answered well enough for my purposes.
Just like with any other religion, when the author of the teachings is no longer alive to clarify what is authentic and what is not, the followers of the teachings will naturally come up with different interpretations and also mix things up with teachings of other religions or belief systems. Even in the time of the Buddha, Devadatta was able to have his own faction of monks. So Buddhism having different schools today is nothing to be surprised about.
The Mahayana school branches out to truck loads of many other schools like Vajrayana, Zen, Pureland etc. It seems to be a natural consequence of not being shy to change the original teachings of the Buddha.  So these days when you say 'Mahayana', it's hard to get an idea of what you really mean.
But if you want to compare the fundamental practices of Mahayana with Theravada Buddhism, here are some differences:

Mahayana puts emphasis on attaining Buddhahood or becoming enlightened while another Buddha is alive. Theravada puts emphasis on working to become enlightened as soon as possible and actually making use of the Dhamma preached by the Buddha to do so, even when he is not alive anymore. Theravada tradition generally discourages those who aspire to become Buddhas out of ego or due to their lack of understanding of the enormity of the task. However, it does give blessings to handful of people who have proven their worthiness through mastery of the Dhamma at the highest level, if they have that aspiration.
Mahayana seems to give precedence to the quality of compassion. Theravada gives precedence to wisdom. Compassion is practiced as a supportive quality of the mind for the cultivation of wisdom.
It appears that Vipassana meditation, the meditation that leads to enlightenment is mainly practiced in the Theravada school. Comparatively, Mahayana school seem to give precedence to chanting, rights and rituals.
Vegetarianism appears to be a requirement in Mahayana. Theravada Buddhism keeps to the word of the Buddha and leaves it up to the individual and does not view one's food preference as an important factor in attaining enlightenment.
Theravada tradition as a principal tries to understand the teachings of the Buddha without changing them to suit the popular worldview of the time. As a result, it is widely regarded as the school which is closest to the original teachings of the Buddha.