Experts predict that India’s population will soon surpass China’s, which will make it the world’s most populous nation with approximately 1.4 billion people.

When exactly this will happen is up in the air. It might have even happened already.

“Actually, there is no way we can know exactly when India will surpass China,” Bruno Schoumaker, a demographer from Université catholique de Louvain in Belgium, told AP News. “There is some uncertainty, not only about India’s population but also China’s population.”

China has been the most populous country in the world since the United Nations began compiling demographic data in 1950.

Yet China’s birth rate has declined steadily, leading to a drop of 850,000 people last year, as The Dallas Express reported. Experts from the U.N. expect a decline of 109 million people by 2050.

The demographic outlook for India is much different, although there are striking differences in birth rates within the country itself.

Women living in the Indian states of the south have an average of 1.8 children, per The Washington Post. Those residing in the north have three.

Despite it being illegal to marry before the age of 18 in India, the United Nations Children’s Fund estimates that at least 1.5 million minor girls are married in the north each year.

Only roughly 25% of women in India participate in the workforce, per the nonprofit Oxfam India.

While India’s economy is booming, the ongoing demographic and economic disparities between the north and south remain a pressing issue for lawmakers, per The Washington Post.

Initiatives have aimed to spark regional economic growth and public health improvements, as well as literacy and employment programs for women in the north.

Yet federal spending and the distribution of parliamentary seats — both linked to population — continue to spark heavy debate in India.

In the past, the government’s response to population concerns involved not only slogans such as “Hum do, hamare do,” which roughly means “Two children only” in Hindi, but also forced sterilizations.

Faced with a growing population, widespread poverty, and food shortages, Indian Prime Minister Indira Gandhi declared a national emergency on June 25, 1975, which ushered in a 20-month-long compulsory sterilization campaign.

Certificates of sterilization were issued. Adults could be denied their paychecks or arrested if they did not have one. Political unrest and widespread panic ensued.

India’s economic liberalization in the late 1980s eventually led to significant growth in the manufacturing and service sectors in the southern parts of the country, per The Washington Post.

Declining birth rates followed, dipping below the “level of replacement” of 2.1 children per woman in the 1990s.

Nonetheless, India’s population is projected to reach its peak of 1.65 billion people in around 2060, due in large part to the northern states.