What can cause the level government bond YTM increase?

economy growing? monetary policy tightens? what else?

Increased credit risk; if currency is linked- fears over depreciation.

Increasing budget deficits

Supply and demand factors
HAve US Gvt borrowing more at same time FEb off loading gvt bonds
Supply is up, price is down, yield is up.

Expected inflation increases
Fear of default increases
Real interest rates increase (demand for money increases relative to the supply)