Harshavardhana invaded the Chalukya kingdom in the Deccan, which was then ruled by Pulakesin II. But the Chalukya resistance proved tough for Harshavardhana and he was defeated. Harshavardhana is well known for his religious toleration, able administration and diplomatic relations.

Political Condition of India after the Death of King Harsha:
After the death of King Harsha in the 7th century AD, India witnessed a period of political fragmentation and instability. The empire built by Harsha disintegrated, leading to a power vacuum and regional kingdoms asserting their independence. This decentralization weakened the political unity and central authority in the Indian subcontinent.

Invasion of Turks:
The political disarray in India provided an opportunity for the Turks to invade. The Turks, particularly the Ghaznavids and later the Delhi Sultanate, took advantage of the weakened regional kingdoms and launched invasions. These invasions were not only aimed at plundering wealth but also establishing their political control over parts of India.

Guarding India from Invasion:
To better guard India from such invasions, several measures could have been taken:

1. Strong Central Authority: India could have benefited from a strong central authority that could maintain political unity and deter external aggression. A powerful emperor or a unified empire could have provided a collective defense against invaders.

2. Military Reforms and Preparedness: India could have invested in military reforms and modernization to build a strong defense system. This would include a well-trained and well-equipped army, fortification of strategic locations, and the development of naval capabilities to protect coastal regions.

3. Alliances and Diplomacy: India could have formed alliances with neighboring kingdoms or empires to create a united front against invaders. Diplomatic efforts could have been made to establish friendly relations with potential threats, ensuring a peaceful coexistence and deterring invasion.

4. Infrastructure Development: Building robust infrastructure, such as roads and fortifications, would have helped in quick mobilization of troops and the defense of vulnerable regions. This would have added a layer of protection and made it more difficult for invaders to penetrate deep into Indian territories.

5. Economic Strength: A strong economy would have allowed India to invest in defense capabilities, maintain a standing army, and support technological advancements for military purposes. Economic prosperity would have also made India less susceptible to plunder by invaders.

6. Social Unity: Fostering social unity and creating a sense of national identity would have strengthened India's resistance against external aggressors. A united populace would have been more resilient and determined to defend their land and culture.

By implementing these measures, India could have better guarded itself from invasions by the Turks and other external forces. However, it is important to note that historical events are shaped by a multitude of factors, and it is difficult to predict the outcome with certainty.

After Harshvardhan death,many kings and dynasties emerged in India and they were fighting each other constantly, and because they were fighting with each other, the turks take an advantage of invading India.

According to my opinion, if India,all the kings and dynasties,would had stood with each other, I'm sure they could hadn't let the turks entered India.