The expedition led by Hamza (ra) who encountered Abu Jahl.
The Prophet (p) sent Hamza on an expedition to Al-Is, near the seashore with thirty horsemen. It is reported from Ibn Ishaq that the Muslims met the Quraysh, their enemy who had persecuted the Muslims in the past and who continued to do so. A battle was about to commence, it is reported that Majdi bin Amr al-Juhani intervened between the two groups, and prevented them from fighting. Both groups dispersed and went their separate ways. Ibn Ishaq:
HAMZA’S EXPEDITION TO THE SEA-SHORE
While he was staying there he sent Hamza b. Abdu’l-Muttalib t the sea-shore in the neighbourhood of Al-Is (T. in the territory of Juhayna) with thirty riders from the emigrants; none of the helpers took part. He met Abu Jahl with three hundred riders from Mecca on the shore, and Majdi b. Amr al-Juhani intervened between them, for he was at peace with both parties. So the people separated one fom another without fighting. 
The above report tells us that there is no mention of a caravan. It is claimed by some that the sole purpose for this mission was to raid a caravan of the Quraysh. Yet the above quote explicitly indicates that this expedition had nothing to do with a caravan.
Moreover, even if the intention was to raid a caravan of the Quraysh, the Muslims had every right to do so historically speaking. It should be noted that when the Muslims fled to Madina, they left most of their possessions behind in Makkah, which the Quraysh then stole from them (Read: ‘Property Of Muslims Stolen – Robbed By Quraysh In Makkah?‘). Consequentially, the above report indicates that the Muslims were not the aggressors. It is reported in a number of hadith that the Quraysh waged war against the Muslims. These incidents took place before the Battle of Badr.
One such incident is when some Muslims, including the Prophet (p) fled from Makkah to Madina. As soon as the Muslims found a safe haven in the form of the city of Madina, the Quraysh wrote letters to the non-Muslim leaders in Madina stating that if they didn’t kill (or expel) the Muslims, they would kill them altogether without distinction:
The disbelievers of Quraish wrote to Abdullah ibn Ubayy ibn Salul and also to those members of the Aws and Khazraj tribes who were idolaters. This occurred while the Messenger of God resided in Medina but before the incident at Badr. The Infidel Quraish said, “You have given shelter to our tribes men, and you remain the more numerous of Medina’s inhabitants. We swear by God that you had better either kill him or expel him, or else we will rally the Arabs to help us and march against you in our full numbers, slaying your warriors and ravishing your women! …” (Ma’mar Ibn Rashid’s Kitab al-Maghazi, page 67) 
There is another narration which speaks about this incident, recorded within the Sunan of Abu Dawud. It is quite lengthy, but provides a wealth of information regarding the historical circumstances of the threats issued by the Quraysh. Sunan Abi-Dawud:
“The infidels of the Quraysh wrote (a letter) to Ibn Ubayy and to those who worshipped idols from al-Aws and al-Khazraj, while the Apostle of God was at that time at Medina BEFORE the battle of BADR. (They wrote): You gave protection to our companion. We swear by God, YOU SHOULD FIGHT HIM or expel him, OR WE SHALL COME TO YOU IN FULL FORCE, UNTIL WE KILL YOUR FIGHTERS AND APPROPRIATE YOUR WOMEN. When this (news) reached Abdullah ibn Ubayy and those who were worshippers of idols, with him they gathered together to fight the Apostle of Allah. When this news reached the Apostle of Allah, he visited them and said: The threat of the Quraysh to you has reached its end. They cannot contrive a plot against you, greater than what you yourselves intended to harm you. Are you willing to fight your sons and brethren? When they heard this from the Prophet , they scattered. … “(Sunan Abu-Dawud Book 19, Hadith 2998)
The full narration for this story can be accessed here.
Notice, the Quraysh threatened to murder and even rape Madinan’s leader’s women if they don’t carry out the order of killing the Muslims. This incident took place before the battle of Badr.
Besides the above report(s), there are many similar incidents reported in our historical Books. Please visit this link to read more about it: ‘Did Quraysh Persecute Muslims When They Fled To Madinah?‘
Consequently, from a historical point of view, it can thus be deduced that the Muslims were not the instigators while they took refuge in Madina. In fact, as has been shown, it was the Quraysh who sought to exterminate the Muslims. Hence, the Muslims had the right to protect themselves, 1400 years ago.
 Ibn Ishaq’s Sirat Rasul Allah – The Life of Muhammad [Translated by A. Guillaume], page 283
 Ma’mar ibn Rashid: The Expeditions (‘Kitab al-Maghazi’) – An Early Biography Of Muhammad, page 67