What Yang Guang never expected was that Li Shimin would be arrogant enough to attack him first.
Just when Yang Guang led Tianxing's army back to Dongdu along the Tongji Canal, the Tang army divided into three groups and began the southern expedition.
The eastern route, led by Zhang Sun Wuji, led an army of 50,000 people across the river from Puyang to the south and marched directly to Bianzhou.
In the middle, under the leadership of Li Shimin, he crossed the Yellow River from Mengjin to the south and approached the eastern capital Luoyang.
In the west, under the command of Yuchi Gong, he crossed the Yellow River from east to west and took Chang'an.
Although the Tang army was approaching fiercely, the Sui army had strict defense deployment and a powerful Yellow River navy.
The shipbuilding industry in the north was far inferior to that in the south.
It was difficult for the Tang army to build a large number of warships suitable for traveling on the Yellow River waterway and to train a large number of sailors.
But for the Sui army who owned the Jianghuai River, this problem did not exist at all.
A large number of warships suitable for the Yellow River waterway and well-trained sailors had already entered the Yellow River continuously through the Tongji Canal.
It didn't take long for Yang Guang to return to Dongfang.
The Tang army was unable to transport grain and grass supplies from the rear to the front, which caused Li Shimin's east and west armies to fall into a dilemma soon after they crossed the river.
Not to mention the army in the middle led by Li Shimin himself, they couldn't even cross the river.
They faced off against the 50,000 Sui army soldiers and 10,000 Xiaoguo imperial guards commanded by Duan Da across the Yellow River in Mengjin.
Li Shimin was afraid that changes would occur over time, so he had no choice but to order the east and west Tang armies to withdraw to Hebei and Hedong respectively.
His decision was timely.
As long as it was a few days later, Yang Guang would make arrangements to complete the comprehensive encirclement of the Tang Army in the east and west.
However, the Tang armies on the east and west routes that managed to escape suffered heavy casualties under the Sui army's pursuit.
They were intercepted and killed by the Sui army's navy when they were halfway across the Yellow River.
All those who could not cross the river were killed.
The Sui army killed or captured them.
The Tang army's attack on the Sui army was easily defeated.
Li Shimin failed to achieve any of his strategic goals, and even failed to capture the Sui Dynasty's granary.
He had no choice but to make hurried defensive arrangements along the Yellow River, and then the main force of the Tang army returned to Jinzhou and Daming in two ways.
After Li Shimin returned to Jinyang to count his troops, he was even more depressed.
Not only did the southern expedition return without success, but he also lost nearly 40,000 Tang army soldiers.
However, what made him feel fortunate was that the 50,000 elite Xuanjia Army and Changlin Army in the Tang Army did not suffer any losses.
He was confident that the Xuanjia Army's fully equipped cavalry, Mo Dao soldiers, as well as the Changlin Army's sword and shield bearers, and strong crossbowmen were the strongest soldiers in the world.
This was also his confidence to launch an active attack on the Sui Army.
Yang Guang did not give Li Shimin a chance to breathe.
Just a few months later, in the early autumn of the sixteenth year of Daye.
Yang Guang personally led 30,000 Tianxing troops and 20,000 Xiaoguo Imperial Guards to cross the Yellow River north to attack Li Tang.
At the same time, in order to ensure the safety and stability of the rear and flanks, the Tang Army's east and west wings were restrained.
Yang Guang ordered Duan Da and Wang Shichong to each lead 20,000 elite Sui troops to cross the Yellow River from Puyang in the east and Heyang in the west, and go deep into the hinterland of the Tang army to raid.
Because they were engaged in harassment operations, they did not have much logistical burden.
The usual battle pattern is that each soldier carries ten days' worth of special compressed dry food at a time, and then attacks the hinterland of the Tang army for five days, a journey of about five to six hundred miles.
When half of the food he brought is used up, he returns to the bank of the Yellow River.
Supplies provided by the Yellow River Navy of the Sui Army could be obtained there.
After Yang Guang and his generals led an army of 50,000 to cross the Yellow River, they encountered almost no decent resistance.
Only when the army had just completed crossing the river, they had a battle with the 30,000 Tang troops who had quickly assembled in Hanoi County.
This battle lasted only After half an hour, the Tang army was completely defeated.
Except for nearly 10,000 people who were killed, the rest of the Tang army surrendered.
After this battle, all the counties and cities in Hanoi County surrendered, and even county officials as far away as Wei County came to offer their surrender.
However, Yang Guang did not go east to Wei County and then north to take the name.
Instead, after arranging the garrison in Hanoi County and consolidating the defense, he directly led 50,000 elite troops through Baixing, Taihang, and entered Changping.
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During this march, Yang Guang was most worried about the two-hundred-mile journey through Baixing, Taihang.
Although Baixing is the easiest of the eight routes in Taihang, it is a mountain road after all.
It passes through countless dangerous passes and canyons along the way.
These places are good places to set up ambushes.
Therefore, when the Sui army marched here, they almost took one step at a time and moved forward step by step.
They conducted forward reconnaissance to ensure that there was no enemy ambush before passing.
Therefore, the 50,000 Sui troops marched for ten days for a mere two hundred miles.
The forts set up every day along the route can serve as strongholds for subsequent garrison troops.
In order to ensure the safety of this logistical lifeline, Yang Guang made an exception and transferred a thousand Beiwei guards from the Tianxing Army to station in these ten camp strongholds together with the subsequent Sui Army.
When Yang Guang saw the relatively flat basin plains of Changping County, he breathed a long sigh of relief knowing that he had safely passed through the Taihang Mountains.
On the entire Longxing Road, there were only a few Tang Army sentries and small camps with more than a hundred people.
Not to mention ambushes, not even an organized force was deployed.
These sentries and small camps were easily removed by the Xiaoguo Army's vanguard battalion led by Shen Guang.
Yang Guang was a little confused as to why Li Shimin despised Bai Xing so much.
However, after some serious thinking, Yang Guang roughly understood Li Shimin's difficulties.
As Li Shimin, he didn't know where Yang Guang's main attack direction was.
Especially under the interference of the Sui army from Wang Shichong in the east and Duan Da in the west who were harassing the hinterland of the Tang army, Yang Guang's main attack direction was even more confusing.
Therefore, it is unknown whether Yang Guang attacked Hebei first and then Hedong.
It is also unknown whether the main force to attack Hedong crossed the Taihang Mountains and entered Hedong, or whether he crossed the Yellow River from Heyang in Guanzhong and entered Hedong.
Even if it is known that Yang Guang entered through the Taihang Mountains Hedong, it is still unknown which pass into Hedong from the Eighth Route of Taihang.
At the same time, Li Shimin should have wanted to complete his achievements in one battle, trying to annihilate the elite main force of the Sui army in one battle.
Therefore, Li Shimin hoped that Yang Guang would extend his supply line deep into the hinterland of the Tang army before concentrating his forces for a decisive battle with Yang Guang.
Therefore, he will not spread his troops on defense.
Yang Guang's speculation was completely correct.
At this time, Li Shimin had assembled a total of 200,000 Tang troops in Shangdang County, Jinzhou, including 50,000 Xuanjia troops and 50,000 Changlin troops.
The terrain of Shangdang County is uneven with mountains and plains.
This is where it is advantageous for the defenders to prepare their positions in advance during large-scale battles.
Li Shimin spent more than ten days carefully deploying troops and building fortresses here, waiting for the main force of the Sui army to fall into this trap.
When he heard the report from the scouts ahead that it was Yang Guang who personally led the army to conquer, he was overjoyed, as if the world was at his fingertips.
Five days later, the vanguard of the 30,000 Tianxing Army and the 20,000 Xiaoguo Forbidden Army had entered Shangdang.
The first people from both sides to engage in battle were small groups of reconnaissance cavalry scouts.
As such small-group encounters became more and more intensive, Yang Guang also knew in his heart that the main force of the Tang army was ahead, and a big battle was about to come
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