Foreseeing the tremendous suffering the Jewish people would undergo during the era immediately preceding Moshiach’s arrival, the sages cried out, “Let [Moshiach] come, but let me not see him” (Sanhedrin 98b).  In other words please spare me from witnessing the terrible travails of the Jewish people at that time.

The pains accompanying the arrival of Moshiach are compared to labor pains.  The Vilna Gaon describes the period as follows:

The redemption is termed “morning,” as it is written, “Morning has come, as well as night” (Yeshaya 21:12). Likewise, it is termed “birth,” as it is written, “For Zion has had contractions and has even given birth” (Yeshaya 66:8)
The darkest time of night is that which precedes the dawn, and the strongest labor pains are those immediately preceding the moment of birth.  So it will be before the redemption.  The exile then will be the most intense of all the exiles (Even Sheleima, ch.11).

In a comment there, the Gaon writes:

Just as in Egypt the oppression increased prior to the redemption, as it says, “Let the work be heavier upon the men” (Shemos 5:9), so will it be in the period of the birth pangs of Moshiach.  The seventy words in Psalm 20 parallel the seventy years of the birth pangs of Moshiach from which [the Jewish people] will be redeemed.

The Chofetz Chaim elaborates on this point:

Before the coming of Moshiach, Hashem will act in a hurried manner so wondrous that even all who are wise of heart will be unable to fathom it.  The troubles and persecutions [of the Jewish people] will follow each other so closely that there will be no space between them.  Just as for an expectant woman who is about to give birth, the closer she comes to the moment of birth, the more intense her contractions and her pain, and this is her most reliable indication that the birth is nearing, so too, the wheels of the era will turn faster at the time of the birth pangs of Moshiach.

The Chofetz Chaim submits an additional explanation for the intensification of Israel’s troubles at the End of Days.  Toward the end of the sixth millennium, the heavenly tribunal will wish to settle all accounts opened since the world’s creation.  G-d will want to prepare His world for its new state, the state of redemption.

This is an indication that the Holy One, blessed is He, wishes to rectify all the old world’s flaws, and to speed up the world’s transformation to birth  of a new world, to the days of Moshiach, in which only those elements of sanctity designated for His name will exist.

Rabbi Elchanan Wasserman also highlights this point:

Since the World will be in a perfected, flawless state during the time of Moshiach, it is necessary for all old accounts to be settled in the period that precedes it.  For piles of accounts have accumulated in heaven from the time of Creation to the present [that is , sins that man has not yet rectified], and they must be put in order before Moshiach comes.  It is therefore the duty of every individual to pay what he still owes to heaven (Ikvesa diMeshicha 18)

The Chessed LeAvraham writes that the intensification of Israel’s oppression constitutes a wonderful process of purification in preparation for the redemption:

Israel’s troubles will become as grave as can be, and they will suffer intense pain.  They will say, of the mountains, “They have covered us,” and of the hills, “They have fallen upon us,” because of the tremendous troubles that will surround them on all sides.  The reason for this is that the Divine presence will judge its household, and G-d will bring them back to the established covenant so as to purify them for the redemption and for the goodness promised to us by His prophets.

That goodness is something the intellect cannot comprehend.  The redemption from Egypt and its accompanying miracles will pale in comparison with the miracles and wonders that will happen to us during the redemption of Israel at the End of Days.  As it says, “They will no longer say, ‘By the life of Hashem Who brought the Children of Israel up from the land of Egypt,’ but instead, ‘By the life of Hashem Who brought up and brought back the descendants of the House of Israel from the northern land and from all the lands to which He dispersed them…’” (Yirmiyahu 23:7-8)

There will then be miracles and revelation of the divine presence to Israel in an amazingly wondrous fashion.  All who merit those times will say, “Behold, this is our G-d in Whom we placed our hopes” (Yeshaya 25;9), literally pointing a finger at the revelation of the Divine presence.  Who will be worthy of this? (Chessed LeAvraham 1:17).

The Chessed Le Avraham goes on to say:

All those who are stubborn and do not repent will perish.  But anyone who bears the yoke of repentance and accepts the troubles without complaint, putting his shoulder to the task, will be purified and become worthy.  The Holy One, blessed is He, is an honest and perfectly just Judge, and there is no injustice.  Therefore, He will refine the person time and time again until he is pure and clean silver. This process will be carried out by the strictest standards of judgment.  In those days, one nation will pulverize another.  Israel will be among them in great suffering.  Each nation will want to shear this sheep [the Jewish people] and eat its meat.  But the Holy One, blessed is He, will have mercy
on G-d’s people through the merit of the there holy Patriarchs, and they will become purified and cleansed as a result of these troubles and this judgment.
(The Ishmaelite Exile, Rabbi Yechiel Weitzman)