In his Haskamah  to the בינו שנות דור ודור of R’ Nosson Dovid Rabinowitz, R’ Yaakov praises the fact that “now Bnei Torah will have access to a knowledge [of history] of which they heretofore knew nothing at all” and that it is good that he is focusing on the Second Temple period of which heretofore each historian had written כאדם העושה בתוך שלו but “now they will see that it is impossible to write on this period without a clear knowledge of the Talmud” .
One example of this is in Megillah 9a in reference to the translation of the seventy wise men - instead of Ex. iv. 20 (on a donkey), "Set them on a porter (man-carrier)". R’ Yaakov asks, Why the great emphasis on which animal was involved? It seems a minor irrelevant detail.
He refers us to Josephus’s Contra Apion , wherein it is written that the Jews were accused of worshiping an ass. He further points to the predominance of the donkey in the Bible (The Messiah is a “poor man riding on a donkey”, Abraham “saddles up his donkey” traveling to the Akeidah, etc.) to explain the source of this slander .
[Update: Ephraim notes that this explanation has already been noted by Maharat"z Chajes in his Imrei Binah (Siman 15). I responded by noting that R' Yaakov actually indirectly refers to Imrei Binah at one point (EY Taanis 31b). He attempts to refute Chajes's position that the Rashi commentary on Taanis was not written by Rashi by pointing out that Tosafos somewhere else cites a Rashi that is identical to the Rashi on Taanis. Since as far as I can recall R' Chajes actually deals with that objection (and answers by saying that Rashi wrote a parts of a commentary that was later incorporated into the larger pirush), I think that R' Yaakov never really read Imrei Binah but saw Chajes's view in his Hagahos to Taanis. ]
See also his explanation of the encounter between R’ Yochanan and the Sadducees (Bava Basra Ch. 8) on the discussion of "ירושה בקבר" in light of the Sadducees denial of the afterlife (cited here).
See EY Yoma 84b in which he cites a Rosh (explaining the Rif) that says that matters of Pikuach Nefesh should not be done through woman and children but rather through Gedolei Yisroel , the Rosh says that this is to prevent מינות. R’ Yakov explains this in light of the Christain slander that the Pharisees valued the law over human life . He approvingly cites the Dorot Ha’Rishonim’s work on this point
In Samhedrin 58b: Resh Lakish also said: A heathen who keeps a day of rest, deserves death, for it is written, And a day and a night they shall not rest, and a master has said: Their prohibition is their death sentence. Rabina said: Even if he rested on a Monday
Rashi notes that he mentions Monday to exclude the Christains who rest on Sunday. R’ Yaakov wonders about this for an Babylonia, as opposed to Israel, Christains were not a significant sector and Ravina should not have found it necessary to phrase his statement to exclude their day of rest? 
Despite all this I see no evidence that R’ Yaakov placed a special emphasis on learning history. His knowledge was of the superficial sort that can be picked up by a vague perusal of Josephus, Dorot Ha’Rishonim and the like. (Cf. R’ Herzog’s analysis of Mar Shmuel cited here that shows an in depth knowledge of the Sassanian dynasty.) Although R’ Yaakov appreciated the value of history to help better understand the Talmud, he never made any systematic attempt to acquire such knowledge.
 Compare the other Haskamahs none of which stress the importance of the study of history - (note that the Rambam writes in Pirush Ha'Mishnayos that the study of History is a waste of time- apologetics like that of Ze'ev Yavetz (History- vol. 12) that claim that in the Rambam's times "history" was all of the "Arabian Nights" variety has been disproven by the discovery of accurate historiography from that period.) See also the Haskamah of R’ Moshe Feinstein to Toledot Am Olam.
 The reader will see that in this R’ Yaakov was influenced by the writings of the Dorot Ha’Rishonim (on this see further below). This book is a worthy successor in both excellence of scholarship (Rabinowitz is clearly proficient in the relevant literature) and regrettably, also in the vicious polemical style. On Halevy’s polemics see Mordecai (ben Yitzchok) Breuer שלש גישות למדעי יהודות and further the criticism of the Seridei Eish in SE vol. 4 דרכו של רי"א הלוי בחקר המשנה This article was censored in the Sefer Zikaron L’ R’ Yitchok Isaac Halevy (See the review in HaMaayan of this sefer.)
 See also the story that Agrippa 1 relates to the mad Casear Caligula to avoid having a statue placed in the Beis Hamikdash (I saw this in the -not entirely accurate- Claudius novels by Robert Graves.)
 R’ Yaakov is clearly referring to the story of the Good Samaritan - Luke 10:25-37
 In this R’ Yakov was mistaken – See here