When any person or group feels offended and attacked, they tend to feel "defensive". Since countries are made up of people, the same "feeling" can occur for the majority of people in a country who have felt maligned and mistreated. Being "defensive" is a form of protection and protest, whether the protest is verbal or through actions. So if Israel is "defensive", you'd only need to look at the history of the country to see how it has experiences "offenses" against it and its people.
Israel is not under "constant attack", although Israel is attacked often. The primary reason for these attacks is that various Arab and Muslim groups virulently oppose Israel's Right to Exist and Israel's treatment of the Palestinians. Of course, there are many in-feeding reasons for these beliefs and they can be read at the Related Question below.
Israel is portrayed as an evil country by some of the media, by many U.N. and E.U. statements, and by much of the Arab and Muslim world.This despite the fact that Israel has better human-rights than any other country in the region (click on the blue text for details).
Israel has been boycotted for decades, and its citizens have suffered from the conflict, yet it continues to be optimistic and it enjoys God's protection.
The presence of the Jews in Israel is questioned by some, despite the Jews' history in and from Israel, and despite God's clear words bestowing Israel to them. Words which are recognized by Islam as well.
Those who condemn Israel for its side in the conflict, fail to condemn the actions of Israel's enemies, no matter how heinous.
See also:
Israel is under constant attack by terrorists, plus verbal attacks by the terrorists' sympathizers. Only a small portion of these attacks are ever reported. Israel's defensiveness is a matter of survival.
They're surrounded on all sides by "enemy" territory, and they can't let their guard down because of possible attacks.
All the main reason was that God had told Israel that you will not have any peace, and so the tribes always attacked each other.
Attacked from all sides
Israel attacked Egypt in response to Egyptian denial of Israeli shipping through the Suez Canal.
Sennacherib and Shalmaneser (V) each attacked Israel in the north, several years apart.
Most of what they gained in 1948, when the UN drew up the map but the "Palestinians" rejected the whole notion of partition and attacked Israel.
Israel
1) In 1956, Israel attacked Egypt with the prompting of the United Kingdom and France. 2) In 1967, Israel attacked Egypt responding to an Egyptian blockade of Israel's southern port. All other wars that Israel has participated in have been brought about due to attacks on its land or its people first.
Israel.
Israel
The Arab countries surrounding Israel have never wanted Israel to exist, and have attacked numerous times.
They attacked Israel within days of its formal creation.
Israel