The Green Line is an expression that is used often in the context of the Israeli-Palestinian conflict and much importance is attributed to it. There is the international demand, that Israel should withdraw from any territories that are located beyond this line and the claim that Israeli presence in those territories is an obstacle for peace between Israel and the Palestinians.
Former US-President Barak Obama demanded in 2011, that Israel should withdraw back to the „pre-67 borders“. He advocated the establishment of a Palestinian state next to the Israeli one with permanent borders that should be based on these pre-1967 lines: „We believe the borders of Israel and Palestine should be based on the 1967 lines with mutually agreed swaps, so that secure and recognized borders are established for both states“ 
Another example for the importance that is attributed to the Green Line is the movement called „Boycott, Divestment and Sanctions“ which was issued in 2005 by the Palestinian Civil Society – over 170 Palestinian NGOs – , who call, among other things, for the „end of the [Israeli] occupation and colonization of all Arab lands occupied in June 1967“  . This movement has grown and gained much international approval since then and aims to put international political and economical pressure on the state of Israel until she follows their demands. Their means include public demonstrations calling for the boycott of all Israeli companies and products located beyond the Green Line.
Interestingly, Israeli companies in the West Bank gave and give work and thus income to many Palestinian workers, and surprisingly – as measured in a very recent survey conducted by Arabs – 43% Palestinians living under the Palestinian Authority want more Israeli companies to open up workplaces for them in the West Bank. 
Despite their prominence, not many people know exactly what these lines are and how they came about. The common understanding is, that they delineate the border between Israel and Palestine before 1967. There is the undertone that if Israel withdrew behind this line, and an independent and sovereign state of Palestine would be erected on the other side, a peaceful co-existence between Israel and the Palestinians would be possible. Yet, if this was the solution, why was there no peaceful co-existence before 1967? And, since Jordan occupied these territories before 1967, why did the international community not call for the withdrawal of Jordan from these areas back then? The assumption of today’s demands for Israel’s withdrawal is, that there was a peaceful co-existence before 1967 and the border – the Green Line – was officially agreed on.
Yet, in fact, the pressure placed on Israel which can be observed today, was already existent before 1967:
„In the 1950s, the Arab world attempted to pressure Israel through economic sanctions; Israeli ships could not use Arab ports, and Israeli airplanes could not use Arab air space. In 1955, Egypt purchased large amounts of weapons from the Soviet Union and Czechoslovakia. [… There were] increased terrorist attacks across the border. […] In May 1967, Egypt expelled the United Nations Emergency Force from the Sinai Peninsula and amassed 100,000 soldiers at the border with Israel.“ 
Economic sanctions were already put on Israel during the times when there were no settlements in the West Bank, no occupied Golan Heights and no occupied East Jerusalem. There were increased terrorist attacks in Israel in the 1950s conducted by Egyptian and Jordanian terrorists in a ‚policy of retaliation‘. Israel sought to normalize relationship with her Arab residents and released in 1966 the military control that she had placed over them. But the Arab World on the contrary re-armed and prepared itself for a war against Israel. Israel attacked her hostile neighbors in 1967 in a preventive war and seized large amounts of territories from the Arab territories. After this war, the Green Line ceased to exist on official Israeli maps. 
It is debatable, if the Six Day War in 1967 was necessary and purely preventive in its nature and there are many interpretations to it. Yet, to assume that the resulting occupation of Arab territories by Israel was the cause for the Israeli-Palestinian conflict and the main obstacle for peace nowadays, is in my view wrong and against logic. From the very beginning and even before its existence the Jewish state per se was rejected by the Arab world, in whatever shape or form. Already before Israel occupied any of the territories that are disputed today, the conflict was violent and very present and no peace was in sight.
What exactly is the Green Line?
In the Historical Dictionary of the Arab-Israeli Conflict, Kumaraswamy explains that the Green Line was the „frontier between Israel and the neighboring Arab states Egypt, Jordan, Lebanon and Syria.“ It was „established by the Armistice Agreements 1949“ and „marked Israel’s borders until the beginning of the Six Day War in June 1967“. It received its name because it was drawn on the map with a green marker. 
On the website of the Israeli Ministry of Foreign Affairs it is explained that the „armistice agreements would serve only as interim arrangements until replaced by permanent peace treaties. […] The 1949 Armistice Lines between Israel and its Arab neighbors came to be known as The Green Line“.
This means, the armistice line of the 1948/49 Independence War was understood as a temporary and interim agreement.
It was open for later territorial adjustments and not demarked as the official border of Israel. Due to ongoing tensions and violent struggles no peace agreements were signed in the following years and a final agreement on the borders was never made.
Cohen, Avner (1996): Cairo, Dimona, and the June 1967 War. In: Middle East Journal, Vol. 50, No. 2 (Spring, 1996)
Kumaraswamy, P. R. (2015): Historical Dictionary of the Arab-Israeli Conflict. Rowman & Littlefield.
 see Kumaraswamy, P. R. (2015) p. 204
 see Cohen, Avner (1996) pp. 190-210
 see Kumaraswamy, P. R. (2015) p. 203-204