The danger of sinat hinam – baseless hatred – the sin blamed by our sages for the destruction of Jerusalem and the Temple, tends to be the Tisha Be’av lesson on which most people dwell, but it may not be the most important one to take from the day.This is not to say it isn’t a lesson worth remembering and applying in modern times. The hatred that the Labor-Zionist movement bore toward the capitalist Revisionist-Zionists, for example, led to a waste of time and effort that could have been put toward saving European Jewry. With the sinking of the Altalena, that hatred brought the state to the brink of civil war at the moment of its birth (thankfully Menachem Begin had internalized this lesson and restrained the Irgun from retaliation).But at a time in our history when we are ready to make dangerous concessions to our enemies, the more important lesson to be drawn from the date marking Jerusalem’s destruction might be a simpler one: We are not invulnerable. Jerusalem could fall again.This very thought occurred to me this past Tisha Be’av. As I did the simple task of washing my hands, I thought of the prohibition on washing above one’s knuckles. I then considered how the people of besieged Jerusalem didn’t even have access to water or food.As a resident of Jerusalem, where I intend to stay for many years, I wondered if that could happen again and quickly realized it could. It already happened in modern times, in 1948. Then, the Arabs put a stranglehold on Jerusalem, intent on conquering one of the Yishuv’s major cities and striking a symbolic blow that could have been the deciding factor in the war.At one point, the city was 48 hours away from starvation.As Larry Collins and Dominique Lapierre write in their acclaimed book O Jerusalem!, “Famine was truly at Jerusalem’s doorstop. Certain elements in the... population were close to panic.” A weed called khubeiza, which sprang up after the rain, became a “delicacy” until it, too, ran out. Arab shelling made it dangerous to leave one’s home. There was no garbage collection due to lack of fuel for trucks. A water shortage was also a serious problem.When describing the even more severe situation of the Jews in the Old City before their surrender, the text of O Jerusalem! reads like a modern-day Eicha: “Their water was almost gone. The electricity supply had failed. The sewers no longer worked and it was impossible to collect garbage. In the May heat, the [Jewish ] quarter’s alleys were heavy with the stench of decomposing excrement.... Uprooted from their homes because the Arabs had either captured them or made life in them unbearable with shellfire, most of the quarter’s seventeen hundred residents huddled together in three synagogues.... They cooked on the floor, slept on dirt-encrusted, vermin-filled old mattresses, weeping, praying or gazing off into space.”Before 1948, Jerusalem was also hit by Arab riots, starting in 1920. And even today, east Jerusalem remains almost off-limits to Jews, not only for political reasons, but also because it’s not really safe there.BECAUSE JERUSALEM is located in the heart of the West Bank, which the world and the Palestinians expect to be the location of their state, the creation of such a state would leave Jerusalem surrounded.Given Israel’s general willingness to make concessions to achieve a peace agreement and past prime ministers’ willingness to cede control over parts of the capital, the Palestinian state will most likely be given some form of jurisdiction in Jerusalem itself.This means Jerusalem will be vulnerable, surrounded and partially occupied by a state whose population views the city as its next conquest. According to the last poll commissioned by the Israel Project, 61 percent of Palestinians reject the notion of two homelands for two peoples, between 66% and 84% (depending on the wording) believe that the destruction of Israel is the ultimate goal, and 92% believe Jerusalem should be their capital.If a Palestinian state is established, Jerusalem will in all likelihood become a battlefield again, whether through rockets, rioting, suicide bombs, roadside bombs, shootings, stabbings or an organized military assault.There are no agreements we can sign with the Palestinians that will prevent this. The Palestinians signed the Oslo Accords and just a few years later launched the worst terror war Israel has seen. Sometimes it is their own police officers who commit the acts of terror.There is also no reliable guarantee the international community can provide. The UN did nothing to carry out the partition resolution in 1947-48; the UN Emergency Force (UNEF) pulled out of Sinai at Nasser’s whim just before the Six Day War; and Security Council resolutions 242’s and 338’s calls for “secure” borders have become meaningless. (For more on this point, see Barry Rubin’s July 24 Jerusalem Post article “The nightmare of international guarantees”).Quite the contrary, the international community usually restrains Israel from defending itself. The fact that the Palestinian state will technically be sovereign will provide it with added protection against Israeli intrusions into its territory under both the UN Charter (Article 2) and customary international law.When conducting day-to-day tasks and working to make ends meet, it may be hard to imagine the hell into which we could descend. That is exactly why Judaism is so obsessed with remembering dates and symbolic rituals and prohibitions. That is why we have a day like Tisha Be’av to mourn past destruction – to remind us that Jerusalem could indeed become a battlefield. It could even fall – it has before.The writer is an attorney from New York currently residing in Jerusalem. He is chairman of Likud Anglos' Jerusalem Committee and a frequent writer on Israeli politics and foreign policy. He can be reached at Daniel@likudanglos.org.il.