[twowords]

My definition of pre-emptive war:

"Attacking an enemy which is expected to launch an imminent attack in order to gain some military advantage in the imminent conflict."

From wikipedia:

"On 26 May 1967, Israeli Foreign Minister Abba Eban landed in Washington with the goal of ascertaining from the American administration its position in the event of the outbreak of war. As soon as Eban arrived, he was handed a cable from the Israeli government. The cable said that Israel had learned of an Egyptian and Syrian plan to launch a war of annihilation against Israel within the next 48 hours. Eban met with Secretary of State Dean Rusk, Defense Secretary Robert McNamara, and finally with President Johnson. The Americans said their intelligence sources could not corroborate the claim; the Egyptian positions in the Sinai remained defensive. Eban left the White House distraught. Historian Michael Oren explains his reaction: "Eban was livid. Unconvinced that Nasser was either determined or even able to attack, he now saw Israelis inflating the Egyptian threat - and flaunting their weakness - in order to extract a pledge that the President, Congress-bound, could never make. 'An act of momentous irresponsibility... eccentric...' were his words for the cable, which, he wrote, 'lacked wisdom, veracity and tactical understanding. Nothing was right about it'."

...

"On 30 May Nasser responded to Johnson's request of eleven days earlier and agreed to send his Vice President, Zakkariya Muhieddin, to Washington on 7 June to explore a diplomatic settlement in "precisely the opening the White House had sought". [42] US Secretary of State Dean Rusk was bitterly disappointed by Israel's pre-emptive strike on 5 June as he had been certain he would have been able to find a diplomatic solution if the meeting had gone ahead. [43] Historian Michael Oren writes that Rusk was "mad as hell" and that Johnson later wrote "I have never concealed my regret that Israel decided to move when it did"."

(Note: the use of the word "pre-emptive strike" is not acurate by the article's own desription)

Two weeks of trops in the Sinai with no attack.
Nasser sends his VP to US to negotiate.
Rusk is "certain" that in fact it was an agreement which was imminient and not war.
Israel manufactures intelligence to try to gain US support for an attack.
American intelligence predicts an easy Israeli victory versus all three adversaries should war break out, regardless of who attacks first.

This was not legitimate pre-emptive war. Israel had more interest in war than in an agreement, so they attacked.

I am only continuing the argument since I hear this given erroneously as an example of legit pre-emptive war fairly often.