Archduke Franz Ferdinand was assassinated on June 28, 1914. A month later, no one was at war. A month after that, 20,000+ were being killed in a single day on battlefields in Europe. By the end of 1914, France alone had suffered one million casualties (killed, wounded, missing, or captured) in the first five months of World War I.
Today, we can do a better job of heading off the kind of all-in response that resulted in those casualties, and the many more to come. But we could also generate one million casualties in seconds rather than months.
Looking at the events during that first month after the assassination, with the delays in communication, the misunderstood messages, the complexities of world politics, and the pent up demand for war among the leaders of many countries, it seems inconceivable that today, with our instantaneous information networks, our simpler balance of power scenario, and our ability to react in a fraction of the time it took to do anything in 1914, we could see anything like the run-up to WWI.
But can we be sure?
Check out the NY Times WWI site. Fantastic.